From what I remember it's ok with atf as long as it's not auto 4wd. (And even those are as long as you don't use auto 4wd, but it's something about the viscous coupling)
NP241s use ATF just like an NP208. I've never seen any of the chain drive GM cases call for gear oil. I don't think the oil pump in them could even move gear oil when it's cold.
He's right about the auto 4wd cases, they take AutoTrak II.