i truly do not think one's record matters unless its like 0-4 or something like that as there have been plenty of guys w/ a 0-0 record or even more losses than wins. i think it depends on how well you impress in the open tryouts and what kind of impression you make personality-wise during the interviews.
of course accomplishments/championships from wresting, bjj, etc. also help one's chances and being undefeated certainly can't hurt. either way, now days you have to fight to get on the show so the best man on paper could potentially lose his first fight and not even get into the house at all (we seen that on season 9 when che mills was deemed the pre-favorite to win the tournament).