I don't like loose stuff in bird cages. Wings go and that stuff is everywhere. I'd also think they'd be tempted to eat that stuff (foraging it it for seeds or something) and it could probably cause a pretty unpleasant problem. I'd say no.
Don't use ground or crushed walnut shells, I know a veterinarian in WA who treated a pair of birds (don't remember their species) that had had ground walnut shells used in their cage.....I believe she lost both birds, but the worst part was that the pair had chicks & the pair had been feeding the chicks the pieces of walnut shells and unbeknownst to the birds owner(s), crushed/ground walnut shells would lacerate their bird's crops.....