Other than the possibility of three-somes, the girl won't be having sex with others, again just interacting with them in ways taught by the councilor. The councilor however will have relations with others through his process, ie the headmistress.
So no, this wouldn't be ntr and people wouldn't generally be upset. Huh, now that you've fully clarified things, it looks like I should try it out and keep an eye on.
If I read the tag rules correctly, I'm not allowed to place tags that aren't actually in the game yet.