"Contracted" in this market is not really all that applicable, unless dealng with Prime morning personalities (Wolf, Don Weeks). Their secondary players aren't generally under "contract".
Nearly EVERY station has jocks sign a "work agreement", geared to protect the employer and do little for employee; Short Version; "I agree to do this, this, and that for XXXX dollars. Employer can fire-at-will and I can quit at any time, but must agree not to work for competitor for XXX days" (usually 180). Pretty standard stuff. Of course it's usually written into agreement that employer can change the terms, increase duties, at any time. If you want to call that a "contact", that is what it is, technically.
There may be something in agreement-depending on daypart- about a "bonus" for reaching 1st, 2nd or 3rd place in the target demo. I believe a lot of employers leave that out of a written contract these days, making a verbal only agreement; i.e., Forget a Bonus.
Things have changed for jocks in this market; a LOT less money and bennies, not many free tickets, more duties, having to agree to much more crap than was usual in past. That may be why you hear so many "green" jocks; they work for a lot less $ and don't know any better.