Identify answers are expected to be as well done as the rest of the answers on the site.
As per example, I give my latest answer to an identify question.
Clean enough where I give the movie I believe it is, and explain with a short paragraph what led me to this conclusion.
Now lets say I had multiple conclusions for what movie it may be. I'm honestly torn on what it should be for that. Having multiple movie in the same answer would be ok, as long as they each are given the same amount of detail for your answer. While posting separate ones will allow readers to more easily see which movie is actually the correct one.
Both ways have their flaws and advantages and we haven't really had a precedent set yet.
As far as what is not allowed, simply linking to an IMDB page while not incorrect will be met with comments from the mods about link only answers and probably a few downvotes from like-minded users.