Here is an extract of Google TOS on this regard:
"General; Serviced Pages; Filtering; Beta Features. You agree not to display on the same Web page in connection with which any Ad Unit, Ad, Link, Search Box, or Referral Button is displayed (a "Serviced Page") any advertisement(s) or content that an end user of Your Property(ies) would reasonably confuse with a Google advertisement or otherwise associate with Google."
So as long as Adbrite ads are not used in such a way that users are confused in distinguishing Adsense ads, you can use both.
In simple terms, if you use different colors/formats for adsense & adbrite, it should be OK with Google TOS.