For testing i see no reason for it not work. The board has many grounds running to the power supply already.
This is surly no worse than testing a board on the box it came in(something many users do).
If you are worried, you can solder a wire from bolt to bolt under the plexiglass and then tie it all to the power supply case with a screw. I do not think you HAVE to, but if it makes you feel better.