How about doing this to every pizza store you encounter that serves meat?
You're not profiting..just wasting a business's resources by misrepresenting your identity and intentions.
Just because you intend to use the 911 hotline as an emergency resource surely shouldn't impede my right as a phone owner from calling it in the manner you intended. It's my god-given right as a phonebook owner to call whatever numbers I see fit in whatever quantities I want to.
It doesn't even have to be 911. You can DDOS the phone lines of any business to make them less effective. Is this ethically defensible?
This is more the equivalent of replying to every piece of physical junk mail that you get using their provided self-stamped return envelopes. I think you'd be hard to pressed to argue that, while being a jerk move, you're still aren't entitled to do it.