"Ranked to match" can mean several things:
1. You are ranked into a dedicated match spot (in other words you are in the top X and there are X residents that they take every year)...in this case you will definitely match
2. You are ranked in a position that the program will typically go down to on their rank lists. For example, you might be ranked #14 and the program typically goes to #15. Then you are "ranked to match" based historically on how low they have to go..there are no guarantees here and if this year the program were to only drop to #10 but you were ranked #14, well you're just out of luck.
So you have to take it with a grain of salt. It's hard to know exactly where you stand on the spectrum. It's a totally different thing if you are told that you are "ranked in the top X" since that is a lot more specific and I did receive calls in both groups. That being said, you NEVER want to tell a program that you are ranking them #1 and then not do it because derm is a small world and that looks very poorly if it comes out that you lied.
These calls are actually totally legit and well within the rules of the NRMP match. Any party can voluntarily tell the other party of their interest and the violation comes in if you SOLICIT for the other's party's interest.