yes, you can place adsense on a proxy site but NOT on the proxified pages. you will lose your account if you place adsense ads on proxified pages.
yes use adbrite in proxy pages/ Adbrite Pays much Better Then Anyother Network. Only Ads Are Not Relevant.
OK, let me clear things up here. You CAN show Adsense ads on the front page of proxies, but then on the proxified pages (ie, the pages people have searched for) you CANNOT show Adsense ads. This is because on the proxified pages people can go on whatever they like (porn etc), and Adsense doesn't allow their ads on those pages. Trust me, I've owned proxies and used Adsense on them long enough to know
I see many proxy sites with Google Ads on, so I guess Google allows you to put Ads on your proxy sites.
You can use adsense ads in main page and in inner pages you can try other networks also . I have seen adbrite ads in many inner pages and those are running well from many months .