I've found it pretty common to have beginners show up at our dojo with experience in other martial arts (myself included). A few of them show some skepticism of aikido's "effectiveness," and some of them leave while others stay. Actually, a pretty significant percentage of the senior students and instructors in our dojo have previous experience in other martial arts to one degree or another.
In terms of these folks trying to resist techniques or use strength, I don't believe I've seen them show any more tendency to do so. Rather, the opposite seems to be true - that those with experience in other arts (that stay) have a tendency to not resist. Maybe because they know from experience in the other art(s) that this could get them into trouble. This was definitely the case for me.
The biggest general difference I've seen between aikido students with experience in other martial arts versus those without is in the attacks they provide. In many cases, those with other martial arts experience seem to be more willing and/or able to provide stronger, more committed attacks when acting as uke. Of course, this is all just my opinion, and I could be completely wrong.