The Church, officially? Nothing. Guido d'Arezzo avoided it because he considered Bb a diatonic note, avoiding the dissonance from F to B. It was nicknamed the "devil in music" for quite some time, but so far as I know there was never any official word on it.
Crazy video. I didn't really get it (and then French isn't easy to understand). It's like he was preaching against rock music. Anyway, if Guido d'Arezzo didn't use the black keys someone started to do so. There in fact many Gregorian chant sheet music with sharps.
To participate in the discussions on Catholic church music, sign in or register as a forum member, The forum is a project of the Church Music Association of America.