Which Might and Magic universe are you referring to?

Sylvan — славянская культура

I doubt it, unless we're talking about a very, very ancient culture... In my opinion, the Gauls would be a better fit.

исламская культура

More likely a mix of Islamic and Indian cultures. Judging by the appearance of most units, they are clearly inspired by their culture, and the names also hint at it (Kshatriyas, Rakshasa), not to mention the war elephants, of course.

или ацтекская (6) культура

I thought they were closer to Africans. Perhaps Aztecs as well, but the latter were much more civilized than Orcs.

Dungeon — ?

I'm having trouble with this one.
They definitely have a Freddy Krueger-esque style. In the sixth game. In the fifth, I would also attribute them to European style, but of a different kind.