lth03, there are many, many kinds of FOWLER tanks, not just aggressive ones, many have reef fish in them, but their owners dont have the time/ money/ whatever for a reeftank, or sometimes just dont want a reef. in an aggressive tank, a harlequen shrimp would probably be eaten quickely, but in a FOWLER fill with reef fish, they would do fine (as long as salinity was kept high enough). this goes for most shrimp.
also, I believe that harlequens tend to leave serpent and bristle stars alone because their tendancy to move quickly startles the shrimp.