Firstly, yes, they should be able to determine if it's Crohn's or not with the biopsies. It's very rare, but not impossible, for Crohn's and UC to co-exist. There have been a few case studies.
I possibly had both colitis and Crohn's. I had typical Crohn's in the terminal ileum, but the colitis part seems to have been more ambiguous. Made a thread about
it on the UC board last year if you're interested.
www.healingwell.com/community/default.aspx?f=38&m=3543814