I think modern rock and alt artists are for the most part, snubbed in general.
The same rock artists are always nominated for everything. And they're for the most part either AC or pop/rock. :P
my faves lol:
However in Canadian awards...I've noticed that Three Days Grace usually gets quite some attention with nominations. So at least one artist i stan for isn't snubbed ALL the time. lol.
Though i'm not going to be a delusional stan and say that Shinedown is snubbed because in all honestly, they really aren't. Their only smash hit was "Second Chance" and that got them an AMA nomination in 09. :P Other than that, their songs haven't done well chart wise or radio play wise, so they aren't really eligible for awards (though i think the singles they've released this year slay some of the other modern rock singles...but that's just my opinion. lol)
Evanescence on the other hand, usually never snubbed. They've gotten quite a few nominations with their hits.
Apocalyptica 7th Symphony was totally snubbed for a grammy, i believe. Because that album was truly a piece of art.
Kris Allen as much as i adore him, he's a one hit wonder (so far) and Live Like We're Dying is the only song that i think could be eligible for anything.

Daughtry isn't snubbed either. For AC rock categories they usually do pretty well and get some nominations. They've even gotten KCA nominations (and for an AC band that's pretty good ^_^)