In the first case, probably yes, as long as you're not rearing cattle to get the manure.Is it ok to use cow manure as fertilizer? It's an animal byproduct. Silk is an animal byproduct.
Silk, except for matka silk (which is only ever taken from empty cocoons) is probably one of the least okay of animal byproducts because you have to boil the pupae alive to produce it. OTOH it's more ecologically sustainable than using petrochemicals to make a substitute which isn't even as thermally efficient, light, or durable.
A lot of the time, the choice is between resources from plants and animals which are alive now (and still just about replaceable) and those which died and rotted centuries ago and which take a lot longer to replace than the rate at which they're used.