This is so wierd that this is my exact scenario!Rabbits DO eat and digest meat, at least in one particular situation: after a doe rabbit gives birth, she eats the placentas, and sometimes also eats any bunnies that died at birth. (Cleaning the nest so it doesn't attract predators.) She digests them just fine. Pretty much all mammals do something similar.
Yes, rabbits need plenty of plants to stay healthy, but they can also eat and digest meat.
(I don't think the rabbits would try to eat the quail, though.)
My doe recently gave birth on Saturday, and today, Monday, I found her- she had killed quail that was in her hutch and was eating it. Does anyone know why? Is it because she lacks protein? What should I feed her?