I think this is a trap card even for Jim Culver. The Cultist, Elder Thing and Tablet tokens are usually worse than Skull tokens only by a bit; usually its around 1-2 points harder. Sometimes they even has the same difficulty and only rarely is it more than 1-2 points. I'd rather take a +1 to all skill tests from a different ally (so you can nullify high negative numbered tokens as well).
The benefit Nkosi has is that you can ignore the effects of the other special tokens which sometimes helps. I don't think this small benefit is worth the cost of 3 (6) exp and a very expensive 4 cost in the ally slot. Seems like you'd be better off taking an ally that gives you +1 Willpower or sticking with Arcane Initiate for more consistency and use your exp for something that'll make a bigger difference.
Might have some really exotic use with naming bless/curse tokens but needs a really dedicated build for it.