If the skin is broken, booking a vet visit is not overreacting. As SweetPotato says, better safe than sorry.
Callused hocks are however very, very common in rex rabbits. Memory foam bath mats in the bunny enclosure often work well. Many types of carpeting are more abrasive to bunny feet than to human feet, especially if the bun does zoomies and binkies on the carpet. I had luck covering the carpet on my bun’s “main transportation routes” in the livingroom and hall with vet bed fleece or soft-ish cotton rag rugs.
I also wrapped my bun’s foot like in this old but still good article: http://www.bio.miami.edu/hare/sorehocks.html
I changed the wrap daily and put on fucidine cream until the sore was fully healed. Then the adaptations I’d made to his living area (he was free roam) was enough to keep sores from reoccuring.
I think you can pretty much skip the part of the article about other causes, because rex rabbits (and some long hairs) have little fur padding on their feet for perfectly natural reasons.