well you can buy those net bags with nesting material in, so dont know what is in there - I would guess its ok as they collect the dog hair from the garden when I am brushing the dogs.
Considering some of the strange things I've found woven into nests I doubt it would do any harm. I put out my dog clippings & they love that!
we once had a sparrow that followed pigeons/doves around & plucked out feathers from their rear ends & flew off with them :o)
I'm sure it won't do any harm. I also empty the carpet fluff my vacuum cleaner into the garden at nesting time and put it on the top of the compost heap for nest-building birds to come and help themselves.