I vaguely recall hearing something about a dual wielding function, but I don't know specifics. One's offhand does not determine one's job.
As far as I know, the only mechanic in the game similar to support jobs is that there's some mechanic for borrowing skills you've learned from other classes. In the Alpha this mechanic was completely unbalanced, and I know they meant to revise it, but I've not heard of whether it made it into the beta or was scrapped altogether to preserve balance.