Angie,

You may end up baffling the sump anyways. Depending on the turnover, the skimmer may end up putting micro bubbles back into the water and up in the display. You really want to keep these bubbles out of a pony tank.

Also, if you have the room in the sump, there is NOTHING wrong with adding Live Rock or Live Rock Rubble to help as part of the bio filtration.

Dave