It's not particularly easy, but you can use it.

Micrometers are best because they are a point-check whereas the jaws on the caliper get in the way. With rotors, the biggest problem is the lip that develops. You can use small spacers to get around the lips (spacers at the pointed ends of the caliper between the jaws and the surface of the rotor), then deduct the thickness of the spacers. Do this at a couple of different locations around the rotor just to be sure you have an accurate measurement.

The problem you then run into is that it's really hard to set the spacer while the rotor is on the car, and pulling them off means removing the brake caliper, etc. It's a lot of work to me...that's why I have a micrometer.

Good luck.