People definitely get admitted from February interviews. Three years ago, I interviewed at Dartmouth in February and was accepted, though I ultimately decided to attend a different med school. (Although I liked Dartmouth very much).
Ad coms have better things to do with their time than interview for the waitlist. They can fill up their waitlist with qualified applicants ten fold without any problem.
If you get a February interview invite, go, unless you already have better options.