I feed the Hikari bloodworms all the time. The little cubes are bite sized for my GT. He eats the whole frozen thing, about 2-4 at a time, but usually less due to $. For my other fish, I just stick in a frozen cube. The top feeders will start picking at it and while it defrosts, the worms slowly fall to the bottom for the tetras & kribs.
I know what Leo's saying about those little shriveled up cubes. My fish don't like those freezerburned things, so they are trash. When popping the cubes out the foil often rips over another one, exposing it to air. I try to use these within 3 days or they will shrivel up. I keep extra packs in the brown bag the LFS puts them in. This seems to keep them good for a while.
About them defrosting, I'd refreeze them and use them quickly. The bad ones should dry out & shrivel up in a couple of days, indicating an air leak.