No rock band should ever align themselves with either a corporation or a politician.
does that include equipment endorsements? Larry's been a Yamaha endorsee since like 1984 or something, and they're one of the biggest corporations in the world.
Personally, I give them a pass on this type of thing, if only because so many other musicians do the same thing. If they're endorsing the equipment they use--especially to make their music--it seems pretty acceptable. It's a niche market that mainly just appears in musician magazine ads--pretty different from having their song be played for truck or beer commercials. Or even iPod ones, for that matter, though that seemed right on the edge of "corporate sell-out" and "very clever marketing for their own album". They've certainly not gotten into that territory as deep as many other acts, and not as deep as they could if they just wanted the money.