I do think this is the phrase that a waiter would say to mean "I am your waiter (for tonight)." Or rather "I am the waiter for this table." So he uses the én so single himself out from the other waiters.
But it's not necessary. You could also say "A pincér vagyok" to show that you are, in fact, the waiter. "Vagyok a pincér" sounds a bit weird, on the other hand.