Actually toothpaste is comprised of materials that are all quite safe for humans to swallow, and doing so helps keep flouride in the mouth longer to penetrate the dentene better. Spitting, not rinsing and ingesting the rest is the recommended approach. That’s not to say I personally do that always, but it’s not because I am concerned about ingesting it.
Some folk have issues with some of the compounds (e.g. flouride) which I don’t agree with, but hey, each to their own.
Whether or not all of these compounds are good for the reef tank is another question. As long as you clean the glass or acrylic well after buffing with toothpaste, I can’t see why you would have a problem. I would think a good water wash, light acid wash followed by another water rinse is more than sufficient.