A great member of a cleanup crew should be the Tigertail cucumber. It mops the surface of the sand with its many appendages, ingesting everything and pooping out clean sand pellets that break apart in the normal current of the aquarium. They can move a lot of sand, enough to make the rockwork shift at times. If you support your rockwork with acrylic or PVC inside the substrate, cucumbers can't cause any issues in your reef.
I added a second picture for fun because the cucumber had picked up a small dead coral branch, making it look like it was saying "Look at me, I'm a snake!" Too funny.
Back in 2003, I purchased one of these cucumbers and over time it has torn itself in half repeatedly, propagating more cucumbers to work the sandbed. There are at least seven in my 400g reef, and they all came from the original one I bought so long ago.