Yeah, they would. Illusion has been pretty clear over the decades that they don't care enough to take action. Otherwise there wouldn't be a giant modding community behind multiple games that have never been released outside of Japan. That is not to say that there is no fault, I'm not going to even get into that, but they won't come after anyone using their assets for other games. That was the whole purpose of the StudioNeo and CharStudio programs in the first place.
Nope, though they did dislike when Fakku tried to enforce on Honey Select 1. Also, yes, that would be the ultimate pairing, make it a foursome, even, with us involved.