When I owned my promotion forum and had team leaders I let them hire. I think if you are going to hire team leaders, you should let them hire there team.
I think it depends on how large the forum is. If it is a large forum then I think you should let the TL's pick who is on their team. Otherwise, I would forget about TL's and just handpick the staff myself.
I don't have 'team leaders', but I let the present staff have a say (and usually it ends up being a vote) on who else is hired. I don't think an admin should make a decision to hire someone without checking with the staff first, just in case there is some sort of major problem with it or something.