Allowed but i doubt they'll accept you. Write a blog, get accepted into adsense, put ads on proxy homepage
Its allowed to put adsense on proxy site homepage but i am not sure if they will accept you if you apply with it . Just create a blog on blogspot , put some articles there and then apply , get approved and then use it on proxy and other allowed sites.
Personally, I don't think you'd get accepted into Adsense if you use a proxy site as the site to get in.