@Majora's
Not all of the production staff does, but Sibsy is very much a brony.
She admits to using pretty much all of the fan names for the background ponies at the studio (Lyra, Berry Punch, etc.) and listening to much of the music, too.
It's a general rule that they're not allowed to read fan-fics, so those are out, but otherwise she's interested.

This blows my Brand New Member mind. If Faust is God, then surely Sibsy is at the least a Saint.