i would say since he is from a high fraud country and has a USC gf , your chances are slim
he can apply but needs to honest about doing buisness with his USC gf and that is a red flag
the CO can assume and probable will that he will come, marry here and AOS to stay
if he did get to come for business he needs to return to Nigeria
if he were to stay and marry, he would not be able to work in the business till his green card was issued
you would be better to do the US part of the business without him
If you want him to come for conferences he will apply for a B1/B2 visit visa. As kris&me noted above, it probably won’t be easy to get especially as he has a girlfriend in the US. The refusal rate for B visas in Nigeria is around 45%.
Hope you manage to have a nice holiday together and not just conference while you are in SA in February !
