I was escorted to my room at the Park Hyatt Vendome by a front desk staffer, and I tipped her. She looked at me a little strangely, but accepted my tip. So after that I realized it wasn't de rigeur to tip a front desk agent, escorting you to your room.

I do tip the front desk staffers at Andaz hotels though when they escort me to my room, because they are frequently also bringing my bags.