carnation's response will probably be better, but here's my $.02:
When I went through recruitment, there was a rumor that PNMs could not be invited back to a certain house after round 3 if they were not legacies there because there were so many legacies to that house. Of course, I know several girls who pledged that house as non-legacies, BUT they admitted to me that they sometimes had to cut even double and TRIPLE legacies because they had so many going through that they would be unable to take any non-legacies if they took all of the legacies.
So, in short, I don't think the release figure method means that non-legacies can't pledge ABC, it just means they'd better be damn good if they want to stand out in a pool of 100s of legacies.
I would assume this is similar with other traditionally strong houses at other SEC schools.