I did some googling, and came across this exact question on a Byzantine Catholic forum.
byzcath.org/forums/ubbthreads.php/ubb/showflat/Number/283675
The resounding answer was yes, deacons can be bi-ritual, and there were a few people who said they knew such deacons. However, what i found interesting was that apparently deacons don’t “need” to be bi-ritual. They can just get permission to assist in another rite, and then they are allowed to. I guess since deacons are kind of “assistants,” they can assist any rite. But since priests are sort of “extensions” of the preaching power of the bishop, they would need to be made bi-ritual, under both bishops. It makes sense. I guess what that means for our thread is that you’re both right; deacons can be bi-ritual, but they aren’t “granted bi-ritual faculties” as such.
Thats what i got out of it. Maybe someone else knows more.