they can. . . as long as you dose around $50 worth of copepods a week. mandarin dragonets need at least 75 pounds of established live rock and preferably a refugium to sustain their diet of purely copepods and their high metabolism. even ones that will eat mysis will slowly starve to death due to the incomplete nutrition that brine and mysis give.
Yes you can, but you need to be an expert level hobbiest who completely understands the needs of Mandarin Dragonets. I've read through a diary of one who kept an MD in a 10g I think. 10g + MD is NOT for new hobbiests or even someone who has been around a few years.