one of the things folks need to remember when considering SH tankmates is that SH spend much of their time hitched and thus stationary, making them easy targets for opportunistic predators/omnivores. this is especially true of sleeping SH, which is typically when these critters are out on the prowl for a meal.
i keep no crabs at all in my SH setups, as i've found that even scarlet reef hermits will latch onto a SH's tail. i prefer to keep true peppermint shrimp in these systems. i know emeralds were mentioned, and when they get some size on them, they can be fairly aggressive.
i kept a pencil urchin in one of my SH tanx for quite awhile, but my wife (seahorsedreams) banished it to the sump when she found it munching on her zoanthids one evening. tuxedos or pincusions are the best choices, tuxedos being the better option IMHO. just remember, those cute little urchins will get some size on them after awhile.
as for skunk cleaners, i've heard of more problems than not when folks keep them w/SH, but as mentioned, it's a crap shoot.
i know in a sense, a lot of this sounds negative, but the bottom line is if you decide to keep SH, you kinda have to tend to their specific needs first, which is why i keep species setups for them with a snail-heavy CUC.
HTH
