I have embers in my sorority and they are great. :) The girls don't bother them at all, possibly because they are so small, peaceful and slowmoving. I don't have aggressive girls, though.
Let me know how you go if you choose a male - I'm hoping to put a male in with the embers and remove the girls later this year. :)
As for RCS, Mo has it right. Lots of moss. Subbwassertang is great, if you can get it. Dense plants like lacefern and hornwort are also good.