Does the Adsense policy allow one to display both Adsense Ads and advertising.com's (ie Aol's) "display network" ads on the same page? Also, am I right in thinking that Google forbids one to use other contextual adverts on the same page as Adsense?
You would be wrong. The only limitation is that the ads must be formatted differently and cant link to forbidden content. Read this for details: https://google.com/adsense/support/bin/answer.py?hl=en&answer=32849