The problem with zinc would be with long term use. The bun could, over time, ingest too much zinc by licking the cream. Sudocreme used to be recommended by vets, but probably mostly for buns with wrapped feet. If the feet are wrapped, the bun obviously cant ingest the cream. You can use plain vaseline as a barrier cream.
When my bun got sore hocks, I used spray-on band-aid, a medical but OTC product intended for protection of the skin under a stoma bandage. Spray-on band aid should only be used on unbroken rabbit skin, on broken skin it stings rather horribly when you spray it on. You can explain that the stinging is transitory to an adult human patient, but not to a rabbit or a small child.
My rabbit vet nolonger recommends cream on unbroken sore hocks. Most creams will just make what hair there is around the area sticky and useless for protective purposes. Buns are also likely to want to lick the cream off, and constant licking of course interferes with healing.
I wrapped my bun’s feet with self-adhesive vet wrap lined with the bun’s own fur. I had to take great care so the bandage covered every last bit of the fur lining, or my bun would pull the fur out of the wrap.