My husband's aunt died of MS, and while I've read that they don't think MS is a hereditary disease, it certainly was a big worry factor for me when my husband was put on remicade for crohn's. In fact, when he developed foot drop, I nearly had them stop the remicade, because I was so panicked. However, it turned out to be a false alarm, he only had some peripheral nerve damage, and he's fine now. I completely agree with you that MS is a bigger concern than Crohn's.
I don't think they recommend that people with MS take Remicade/Humira/Enbrel/Cimzia - it does have the possibility of making MS worse, and I wouldn't take it. There is a medication called Tysabri that can help both the crohn's and MS - though I think it also has some scary side effects (I seem to recall in the news). I'd look into that one rather than the ones in the remicade family.
Husband with Crohn's
Diagnosed March 2003 Ulcerative Proctitis
Diagnosed March 2008 Crohn's & C-diff, hospitalized 45 days
Canasa, Lialda, Remicade, VSL#3, Florastor
In Remission since June 2008
Stopped vancomycin for c-diff Jan 1 2009
C-diff free, and in crohn's remission, knock on wood