Originally Posted by Fat Solace
Just teach it in the Gen IV game then, to be safe. You don't want to get DQ'd over having it from the BW2 game unless TPCi says that they'll allow BW2 tutor moves to be used.
Conversely, if you want, an easier option would be to just make the mon in gen 4 and then do whatever you want with it. For example, any gen 4 Larvitar can be leveled / eved in a 5th gen game, transferred to BW2, and tutored there.