I think Amazom Associates is not Contextual (I thinks it means "Content Targetting") , So It's welcome to put it on same pages
http://forums.digitalpoint.com/showthread.php?t=74630&highlight=adsense+amazon you can find your answer there...
I have using both together, but come to think of it, aren't some Amazon links contextual? The keyword-based best sellers for e.g.? I use those a lot.
As dcristo said it is not against TOS to use amazon with adsense. As long as the ads are non-contextual you can use them. You can also use chitikas new ads with Google as they are also non-contextual.