I dunno.
My impression of Brendon from the last two seasons of BB-US is that he'd likely be a very competent Racer both physically and mentally (a lot of people forget that Brendon stayed in the BB House after Rachel was evicted in their first season, and the winning alliance kept him as long as they could before getting to the final three that summer; and Rachel while a bit more emotional in her gameplay was quite competent in the BB competitions last summer.
So without knowing the other teams or anything else, one could see them doing well if Brendon and Rachel keep their cool and focus on the Race.
As far as recent BB contestants go, I'd rather see what Hayden Moss could do on TAR.