Freezing will, of course, not kill microbes. That has been established.
Most fruit companies do a reasonable job of washing the fruit before they freeze it. This will cut down on the "microbe burden" of the fruit without eliminating said burden. If the fruit is being added in the secondary (or even tertiary or quaternary or... fiver-ary
) phase, then the yeasty-beasties have a good, solid foothold and should be able to kneecap most competitor beasties who catch a ride in courtesy of a sloppy washer robot at the Dole factory.
Soooooo... is frozen fruit sterile? No.
Is it safe to add to secondary (or tertiary, or quat -- NOT THAT AGAIN)... Yes. Should be fine.
Don't do it if you are submitting to a contest, though, or if you are a perfectionist. Boil it like the good man says if it makes you feel good. Or if the voices tell you to. Best not to irritate the voices... they can get sooo cross.... you wouldn't like them when they're cross....
Cheers.