I have never kept dwarf seahorses but I did raise erectus fry once. I used Dan's Feed with beta gluten to enrich the bbs. Dan's Feed is from Seahorse Source.
I use Dan's Feed to enrich live adult artemia and ghost shrimp as well for my adult erectus ponies. I never try to enrich frozen mysis as I feel most of it just washes off and degrades the tank water. Some seahorse keepers do use Vibrance from Ocean Rider. They sprinkle the vibrance on the frozen mysis and allow it to soak in. Then they rinse off the excess and feed. Pete Giwonja, a very knowledgeable person on seahorses subscribes to that method.
I enriched frozen food, maybe two or three cubes a week with either Selco or vita-chem. I've only done this for maybe four months and my seahorses bred for the first time (in a year and half) about three months ago. Can't say it's more than an anecdote but I do think it's good to enrich frozen food. I rinse it in a net and a little bit of ro/di water but when I don't enrich I usually don't rinse the frozen cube.