Can You Perform a Gum Graft Over Existing Veneers/crowns?

One can only graft over root surface not enamel, veneers or crowns. There is no attachment mechanism over porcelain and enamel and the only thing one would create, in my experience, are deep pockets and new sources of inflammation. 

Grafting of gum cannot be successful over veneers. One option is to remove the veneers and place temporaries, graft the gum tissue, and then place new veneers shaped and of a length you desire. Most importantly, the cosmetic dentist and the patient should communicate clearly the goals prior to beginning the case.

Many of the wonderful advantages to modern dental techniques can be viewed as disadvantages as well. Lasered gums likely will not grow back, and grafting gum tissue won't stay on porcelain.

While the complaint to the royal college may feel satisfying, there likely won't be anything from it. The best move would be to seek a second opinion on what your options are.