I think KG is a "dirty" player, to the extent that he does things to get under opponents' skin. He definitely gets in extra contact after the whistle, or when the refs aren't looking. He fouls hard, and a lot of times he pushes the envelope.
The thing is, a lot of great players do stuff like that. Kobe does that, for instance. Shaq did that in his prime, and still does it. Dwight Howard does that. The borderline plays often give a team a physical and psychological edge, and that's often part of winning basketball.
Where I don't think KG is a "dirty" player is in terms of things like intent to injure. I've never seen KG intentionally attempt to harm somebody (well, outside of maybe Wally Sczerbiak or Rick Rickert). He's seemingly always known where that line is drawn. You don't see KG repeatedly trying to stick his foot under jump shots, for instance, and KG doesn't get ejected from many games due to rough play or flagrant fouls.
In my mind, the first type of "dirty" is perfectly acceptable, while the second type isn't. So long as KG continues to not tread over the line, I've got no major problem with his play. (I do worry during the few times when he loses control, like when he was suspended in the playoffs last year, or when he made contacts with the refs this year. Those things are not, in my mind, a necessary evil. However, I chalk them up to momentary losses of cool, rather than premeditated dirtiness.)