Hi, this is my opinions as somebody in the pool business for 8 yrs but never applying plaster myself. First you might want to let the contractor use his preferred guy so that he is always the one liable if it does not come out right. Second if the old plaster was prepped properly the chance of the new plaster flaking off the old plaster is very slim. Thirdly, there should be noticeable changes in the "elevation" of the plaster around the tile and fittings if the second and third plaster was applied at the proper thickness. A sub, if it is a replaster at there expense might put it on as thin as possible. (if a plaster guy tells you anything different than what I've said, take his opinions over mine)
