No, rex is co dominant so the "hets" are the ones that have curly hair. Homozygous rex or double rex are almost hairless. You shouldn't have any of those unless you breed 2 rexes together.

You can breed any single rex to any normal coat rat and get 1/2 rexes.

I have a hairless male that I am hoping is a double rex so I can breed him soon and get some rex coats in my rat lines.