Sorry, never been in that particular situation, but 'team dinners' are fairly common. If you were the only one on the 'team' then maybe...
You'd really be the only one that could judge romantic interest, like the above poster described. If there were signals or even hints then I'd def politely decline. If your relationship was strictly professional and perhaps you mentioned wanting to pursue training in the same specialty as the preceptor, he/she could genuinely be looking to play a mentor role. Even then though, I'd try and turn it into a lunch or brunch thing rather than dinner.