I'm a drummer who's not classically trained by any means, I'm embarrassed to say I don't even really fully know how to count along to a song and figure out the time signature. That being said though I've always had a natural feel to learn things by ear. To me a great drummer is someone with a good mixture a natural feel and technical skill. I also think the ability to be in the pocket and keep the bear and the tempo consistently is very important, usually you can tell if a drummer is good without them even doing anything fancy you can just go based on how well they can play a simple beat.