I'm a big user of live foods, against what alot of others subscribe to, especially in breeding situations. I'd prefer the live over frozen as I'm sure most fish would, except maybe lazy ones lol
But, like Lupin said, I'd shy away from the tubifex. They tend to hang out in some less that savory places.
There were however, tubifex present at the site I started my Pond/ramshorn snail cultures from but those original snails are at least 6 generations removed from my culture.