I like your question, but if you think about it in a logical way, anything that is alive you will have to take account for on the biological load. But personally, I wouldn't think that hermit crabs, or clean up crew for that matter will take a heavy toll on it, but all in all total, maybe the amount of a decent sized goby. Overall, they will help the load by eating leftovers, but also they are living creatures. Overall, I wouldn't worry too much about them though. I would focus more on the fish, but maybe keep one less fish than recommended to make up for the load, your call. With proper feeding and water changes, you'll be fine.