When we used Al Maha for visitors recently they met them at the building entrance as they got off the bus from the plane.

However, I think flingwing wants to know where the travel agency driver will meet him, no Al Maha. I expect they'll be in the area through the doors directly after you've picked up your bags and had them screened, along with a million other people waiting to pick someone up! They'll most probably have a sign for you.