Can someone get a gingivectomy when they have porcelain crowns?

Yes: A gingivectomy (removing some of the gum tissue) can be done around crowns. If these are crowns on front teeth, then the dentist (either a cosmetic dentist or a periodontist-gum specialist) will need to use a lot of finesse to avoid showing root structure which can be unattractive. For these cosmetic procedures in our office we use a laser for high precision.

Yes: Having procelain crowns has no bearing on getting a gingivectomy. The only problem may be the exposure of the margin of the crown which may affect the cosmetics.