I've given mine a small dab of natural peanut butter several times, and there hasn't been a gill issue at all. I suppose it's possible, but it shouldn't be a major concern.
As for peanut butter powder--mine love it! I've got a 'mix' I've made for them (they only get it for a special treat) with oats, peanuts, dried strawberries, eggshell (for calcium), and peanut butter powder. I mix it with a drop of hot water in a small seashell and they devour it!
If you have a pesticide-free yard (or know someone with one), you can get all kinds of stuff for them to forage. Just today I got mine wild peas, wild blackberry leaves, maple buds, dandelion, and clover!
Another idea to give them some variety is to give them scraps of whatever you're cooking (just each ingredient is best, as most seasonings aren't the best for them).
One thing that many crabbers have in their tanks that the crabbies love is worm castings. I keep mine in a separate dish all the time (it doesn't mold or anything). While many Etsy sellers have it, it's more economical to just head to a garden store, nursery, or even a hardware store, where you should be able to get a good-sized bag for only about a dollar/pound.
Something else I've given mine recently that they love is spray millet (in the bird or rodent section at petstores). Make sure it's not flavored or colored. I've stuck several pieces in this cholla arrangement we call the 'millet tree', and it's their favorite hangout spot!
Of course, you can totally buy lots of little Etsy foods; that's great. But if it's not in the budget, there's lots of other unique/creative things you can feed your crabs. Just check out the safe:
https://www.hermitcrabassociation.com/p ... 25&t=92557 and unsafe:
https://www.hermitcrabassociation.com/p ... 25&t=92556 care sheets, and make sure they always have a source of protein and calcium.