Well I prefer live BBS because I believe it's healthier/more nutritious, I have no problem hatching them, it's cheaper, and it's more fun watching them chase down the live, swimming shrimp, haha. But also, the live BBS will live for a while in the tank, so the feeding lasts longer, I can slightly overfeed without worrying, as they'll eventually eat them all (as long as I don't overdo it), the frozen will just sink to the bottom (this also keeps the fry off the bottom, scavenging for what didn't get eaten on the way down). What problems did you have hatching the live BBS? I have zero problems and it takes all of 2 minutes a day to setup.
However, frozen would be an ok substitute assuming your fry will eat them (which you say they are), so I don't see a major problem with it, if it's easier for you.
Linda