Menstrual blood or pole:
According to Hart, auspicious and in-auspicious traditions are defining paradigm of Tamil society. Therefore, the name of the untouchable caste in South India, Holeya(Kn) or Pulayan(Tam), is derived from a word pole which meant menstrual blood or pollution due to menstrual blood. As South Indians held menstrual blood inauspicious because it was uncontrolled just like spirits of Holeyas.
But I would like to know if the meaning menstrual blood is primary or later day derivative. If you check various branches of Dravidian languages this word is attested as menstrual blood only in SD-I, rest all have (ND(Brahui), SD-II(Telugu)) the present meaning of unclean or dirty. Curiously, pole meaning menstrual blood is not attested even in Tamil(part of SD-I).
According to Hart, most of the Southern languages have some equivalent for Tamil pulayan to designate outcaste. Well, "most" is a very ambiguous word. Anyway, Telugu does not have any equivalent for this word for a man of lower caste. And Telugus make up one third of Dravidian speakers in India (more than Tamils).
The Telugu equivalent caste for Kannada Holeya or Tamil Pulayan is called "Mala". I am not sure of the etymology of Mala. So let us take an indirect way and try to understand the terms for the people declared unclean or untouchable. We can consider two meanings from Hart's pole and general meaning of pole;
1. The people with uncontrolled traditions therefore word meaning polluting menstrual blood which is also uncontrolled.
2. The people are unclean therefore the word for unclean
If we consider the first meaing then we have to find menstrual blood meaning for mala. I have not found that. But the second meaning is very close if we take the word mala is in fact a borrow from Indo-Aryan language. The IE root mel* means unclean, dirty(malina in Sanskrit). The mala could be an exact equivalent word for Dravidian pole in Indo-Aryan. If mala is indeed an Indo-Aryan word then we can be sure that a big chunk of Indo-Aryanized population from East(predominantly Y-Haplogroup H, and Y-Haplogroup R2) have already become part of Dravidian peoples since the dawn of their civilization. Therefore, ritualistic impurity and consequently untouchable status of people in South Indian society need not be autochthonous to South Indian society.
Now let us consider the unclean menstrual blood itself. I have already said that could never be part of pure Dravidian society as it never developed concepts like linga and yoni. So the best way is to understand old North Indian and East Indian attitudes towards menstrual blood.
Excerpts from Manusmriti:
A Kandala, a village pig, a cock, a dog, a menstruating woman, and a eunuch must not look at the Brahmanas while they eat.
For the wisdom, the energy, the strength, the sight, and the vitality of a man who approaches a woman covered with menstrual excretions, utterly perish.
Let him not sleep alone in a deserted dwelling; let him not wake (a superior) who is sleeping; let him not converse with a menstruating woman; nor let him go to a sacrifice, if he is not chosen (to be officiating priest).
Let him never eat (food given) by intoxicated, angry, or sick (men), nor that in which hair or insects are found, nor what has been touched intentionally with the foot,
Nor that at which the slayer of a learned Brahmana has looked, nor that which has been touched by a menstruating woman, nor that which has been pecked at by birds or touched by a dog,(A woman) is purified on a miscarriage in as many (days and) nights as months (elapsed after conception), and a menstruating female becomes pure by bathing after the menstrual secretion has ceased (to flow).
When he has touched a Kandala, a menstruating woman, an outcast, a woman in childbed, a corpse, or one who has touched a (corpse), he becomes pure by bathing.
By earth and water is purified what ought to be made pure, a river by its current, a woman whose thoughts have been impure by the menstrual secretion, a Brahmana by abandoning the world (samnyasa).
I shall stop it here. From the look of it every attribute that make menstrual blood inauspicious could be found in Manu's laws. Therefore, unclean menstrual blood is secondary meaning to pole. Probably, after the migrations of Indo-Aryan peoples to South India who became Dravidians(and who could be Austro-Asiatic, Burushaski , Caucasian speakers before becoming Indo-Aryan speakers).
Warriors and auspicious power:
This is quite interesting to me. The othreday I was watching a documentary on Qin Shi Huang, First Emperor, who unified China in 221 BCE. The emperor (or his Shamans) had to take care of spirits of dead enemy soldiers from being harmful after their successful attacks. A typical Soulistic society must show this characteristic. The spirits that are harmful are that of your enemies. But in South Indian society more than the spirits of dead enemies(if at all they do), it was the spirits of dead native soldiers that were dangerous. According to Hart, warriors were themselves source of power and they were not harmed by spirits of enemy soldiers. But spirits of these warriors by themselves dangerous to the natives and had to be propitiated. No wonder with this kind of logic the soulistic society made room to godistic society whereas China even with those inauspicious spirits remained unified and was never really a godistic or auspicious society.
Funnily, Holeyas in Tulu society were soldiers at least till 15th century(Afterwards none of the local Tulu communities participated in warfare. The region came under direct control of Kannada rulers during this period who did not trust the natives and settled Marathis there for soldiering). According to some records, they(Holeyas) were even generals during 3rd-4th century. Later the army chiefs were mostly Bunts and sometimes Billavas. However, every community be it Billava, Bunt or Holeya had to send a person from each household whenever there was a war. I wonder how a Holeya in Tulu region who at once was a source of power(as a warrior) and also a receptor of a power(because he was Hart's Pole derived Holeya) fit into this whole auspicious-inauspicious scheme.