I've seen stores and talked to people who say 1 hermit per gallon too. That always seemd a little extreme to me. I've got a 75g reef, and I currently have 8 blue-legs, 7 scarlet reef hermits, 1 emerald crab, and 10 turbo snails. They seem to do a pretty good job... algae is kept to a minimum most of the time. If anything, I think I could use a few more (maybe 5) turbo snails. At times algae tends to build up on the glass. No biggie though. For a 75, I'd say go with 10 blues, 10 scarlets, and 20 turbos. That should keep algae at bay.
Good luck.