A belt sander is a better choice than a ROS due to the likelihood of chipping out the edges. But if you apply little pressure and start with 150 grit and finish with 400 you will likely be fine. You can spray the pad with a light oil to help in the latter stages. Best to try it first on a scrap of mirror or glass to get the feel for it. If you don't have any scraps, a local glass shop will usually be happy to give you one.
Hope this helps,
Phred