Sometimes the 3rd poison is translated as "ignorance," sometimes as "indifference." Are these both alternate translations of the same Tibetan word, or 2 different words?
I am not sure if you are referring only to Tibetan usage, or rather English translations of Tibetan usage, or if you are referring to the three poisons in any tradition. Not knowing Tibetan, I cannot comment on that. But from the Pali, Sanskrit and Chinese, I can see no way that the third poison could ever be rendered as "indifference".
There are basically just a couple of forms of the three (sorry, I'm mixing Pali and Sanskrit below):
The first is greed (lobha), taint (raga), or maybe thirst (trsna);
The second is anger (dosa), aversion (patigha);
The third is usually either delusion (moha) or ignorance (avidya).
I have never seen any formulation which has anything like "indifference" for the third, and rendering either moha or avidya as "indifference" is just plain incorrect. And I don't mean incorrect as in a bad translation, it simply is not a translation at all, but a completely different word.
So, is this a Tibetan language issue? I'm curious...