It's pretty hard to keep an eye on them at night. Nighttime is when I had most problems with them, and I had serpents because I thought them to be far less aggressive than brittles. IMO, it is NOT worth the chance as it's not YOUR life at stake, but that of the seahorses.
People told me just keep lot's of food in the tank for them and I would be OK.
However, that seriously degrades water quality leading to bacterial infections.