Ok so i solved the messed up uv's when importing in C4D by selecting the 3ds Max preset in the OBJ import window !
But now i have 2 more problems :
-the first one is that seams appears at each island's border. I haven't put any seams with the same named tool in the retopo room but thought this was just to "relax" the island when unwrapping, in places where there are sharp or narrow shapes...
-the second one is that displacement doesn't seems to do much. I tried increasing the strength, height etc with no luck...
Rgr2005's post in [Solved] Incorrect UV Mapping in C4D problem was marked as the answer