As far as I know there are no particular requirements, other than passing Steps 1 and 2 and graduating from medical school. However, you may want to look at each program's website to make sure--they'll spell out any specific requirements (but they're usually things like a minimum USMLE score, etc.). I don't remember interviewing anywhere that required a particular rotation (other than the general ones you do during third year).
With that said, I believe no one going into a prelim-IM or TY should go through 4th year without doing at least one medicine sub-I. My school required two sub-I's--a floor month and a unit month. I'm very glad I had to do both.
Also, one thing to keep in mind is many prelims specifically want a letter of recommendation from the chair of medicine at your school. I don't know how much of a difference it actually makes--I just heard it was important, so I got one. Doing a sub-I gives the chair more information to work with.