yes, tunicates are good. they are pretty much exactly like sponges in thier requirements. just a different branch on the animal tree.
Chris- do not know enough to make that assumption, but in our systems they are. most of the sponges we find in our systems coat the undersides of our LR. tunicates will usually hang out in the higher flow areas. the overflows, sumps. they seem to be able to handle light a bit better than the sponges. it could also be the fact that they can move, so the algae may not be able to get a foothold.
i do know however that some of the open water sponges can get very tall, so i know that assumption is not totally true.