In most instances, yes, they are homers. If you watch any White Sox games on WGN, you'll see some of the worst. Hawk & DJ are two of the biggest homers I've ever heard, and listening to them annoys me to no end.
There are some who are better than others. Vin Scully, who calls Dodgers games, is a great announcer. I don't hear much homerism from him, and he's a great storyteller.
I'm from Cincinnati, and the guy who does local radio here is Marty Brenneman. While I often don't agree with what he says, he definitely has no problem stating what's on his mind, including when he thinks the Reds did something stupid.