In the loose sense of 'form' (cf. Physics I.7), I think objects could: a rabbit has the form of a rabbit, and if it's white it has that form too. That's also consistant with the relationship between primary and secondary substances and non-substances from Categories.

On the other hand, in Metaphysics, 'form' is pretty much restricted to the identity of a substance. Still I think Aristotle would be happy enough with polymorphism so long as you made a distinction between substance-forms and non-substance-forms.