Replacing old fan switch with no ground terminal
You'll need to do a bit of digging and wirenut a pigtail on that ground, but yes, that is a ground and should be used to ground your switch, as well as the box if it isn't already hooked up to said box.  All metal things associated with a circuit hook up to the circuit's ground wire, by the way, so you can still hook onto it if it's grounding something "down the line" -- as long as all the cables coming in are connected to it, all the downstream boxes and devices will still be grounded.