Yes, I think an eldar would quickly spot the psychic taint of the genestealer infection. Likewise I'd bet a space marines super immune system would reject infection. As to tau, they are almost certainly infectable, but their very socialist lifestyle would make it hard for the infected to deviate and breed secretly, and their medical science would likely detect the infection quickly or at least aberrant behavior. Also, given the tau aren't too impressed by psychic powers could that whole genestealer "Hypnotic forget this happened" thing work on them? Plus could ethereal control override their enslavement to the genestealers?
I think we need to assume orks are immune to genestealer infection, else at the rate orks breed the hybrids would have taken them over by now.
Nope! back in the old days (the 90s) there were ork-stealer hybrid models by GW.
3d row down , 3d from the left: Genestealer hybrid.
Edited by Robin Graves