No ballerinas do not wear any bras under their outfits.
The way the Leotards are designed there really is no way for a ballerina to wear bras under them so ballerinas do not wear bras under their outfits.
Ballerina leotards are made double lined and have some support and/or are worn very tight and they do not need the additional support of a bra anyway.
It's basically impossible to wear a bra under a ballerina outfit with the way they are designed.
Well actually you could wear a bra under your leotard if you wanted too but it would be uncomfortable if you do wear a bra and there's really no need for a bra.