When we were planning our VR our land coordinator said that it was not necessary to tip the captain, coordinators or musicians, that it was all in the price, at that time it was$1,000. and a great bargain.
However, we did print stationary Thank You cards that we had our cruise coordinator put in each of our guests cabins.
At the end of the cruise we did have a monetary 'Thank you' for our cruise coordinators, Rodrigo on the ship and Cathy Ingram at Franc's. Unfortunately I do not remember how much.
If your event is perfect in every way then I would suggest, if its in your budget, to give them a monetary gift in a card.