I think that LA build is probably an old QA build.
But I also think, given that we've already seen lizardman, that it's patently obvious that there's at least one more unlockable character, and thus the 4 slots do not correspond to DLC.
If the NYCC build is indeed the final retail build and Azwel is locked, I think we can decide for sure whether any of the 4 slots are for DLC. Just have someone hover over the slots, and see if the UI says anything like "this character requires an additional purchase" or "this character is DLC" or "pay up bitch". If a slot is DLC, it's going to be clearly labeled as such. To do otherwise would create massive player confusion, if the locked DLC slots look identical to Azwel's locked slot. Players would be thinking, "Great, I unlocked Azwel, now to unlock those other characters whose slots look exactly like his did!" It would be a grossly obscene UI fuckup.
If one of those slots is, in fact, for Tira, hovering over it will tell players to go buy Tira, since she's day 1 DLC.