A Blue Linckia starfish is one of the only reef-safe stars I know of...they may come in a maroon variety as well. Just don't get a white burrowing sand star. I still have yet to find someone to take mine (they chow on sandbed fauna)
Don't know if this helps with the Orange Knobby id, but MarineDepotLive has a Africian Red-Knob Star id'd as Protoreaster lincki at http://www.marinedepotlive.com/1304034.html
(note I didn't typo the name, it isn't African but Africian on their page).
I got mine from a MO in Canada. Was just getting one for a small tank, but liked it so much I ordered two more, since traded one to a fellow reefer. The MO said his customers said it was a good reef star, so I tried them. As I say, they are fantastic.
Interestingly enough, his supplier listed them as a red starfish. They are definitely orange, and FFE has the only pic that looks just like them, listed as an orange knobby.
They are detritus eaters, and will clean into the holes in the rock, cruise the surface of the sand, spend some time on the glass, and also eat nori and algae pellets. I love them, and when he gets more, I think I'll try a couple in the refugium to see if they might breed.
yznhmr: I got mine in Canada, so that doesn't help you, but check this out:
they can't guarantee availability, they may give you a red fromia, but I have heard much good about them as well. Or perhaps they would let you know when they get some in.
I have a blue linckia starfish and it is awesome. The blue is so bright. I know some people say they have trouble adapting them into the tank. I had no problems with mine. Good Luck.
I am not an expert on this topic.
When you take any animal out of its natural habitat and add it to your tank, there is the chance that you are giving it an oppurtunity to do things that it wouldn't do in the wild. If you aren't feeding your starfish, then it may very well go after food for itself. It is in an enclosed area, so it has the choice of starvation or finding food on its own. I am still trying to find a starfish I think would be happy in my tank.
I have a small brittle star, about 6" across and doesn't seem to bother anything. I have never seen it come all the way out from beneath the rock crevise that it made its home. I do however feed it a piece of shrimp every so often.