Brock was a money making gimmick Dana White brought in when the UFC was having trouble with Randy Couture. Randy's leaving with the title, the success of foreign fighters aquired from the PRIDE buyout, the rise of other American based fighting organizations with TV contracts scared Dana that he might lose his key market demographic (12-40) year old white American males.
Dana, being a smart businessman, reacted by changing many of his sponsors including more "pro-military" "pro-american" businesses. Going to the wrestling well was genius move...not from a purist standpoint, but certainly from profit one. Brock agreed to "play his part" because he is an actor and Dana helped to make him legitimate by supplying the trainers and giving him a title shot so early.
It's as much a gimmick as bringing in a "boxer" or giving a Youtube street fighter a shot in the ring. I'm waiting for the Brock vs Brown bear fight!!
Anything to hold onto that demographic that buys the PPV, clothes and whatever else the sponsors are selling.