Yes, and I wouldn't. First, you'll have some nice, fragrant, rotting shrimp to contend with. Really? You'll get just as good a start with flake food. Plus, you've got your fish to help you along.
Don't you have a Freecycle group in your area? Go to Yahoo > Groups and type in Freecycle. Then look for one in your area. Just post that you're looking for some mature aquarium filter media and see what happens. Maybe you could even trade for something (but don't put that in the post as it's verboten on Freecycle).