If I could nerd out for a moment, P. syringae is an interesting organism; it evolved the highly effective ice-nucleation protein so that the ice would form on the surface of a plant, which bursts the plant cells open, which then the germies eat. I remember, in the 80's, someone tried to field-test a strain that was genetically engineered not to do this, to decrease crop damage due to frost; looks like they were never able to market it. P. syringae has also been found to be responsible for a significant amount of cloud formation, so we owe them much more than snowmaking.
So, although P. syringae is technically a plant pathogen, it is, literally, "everywhere", and using its ice-nucleation protein as an additive cannot be adding much to what's already out there. Still, even if it is naturally-occurring, we should at least be thoughtful about spraying our little playgrounds with anti-anti-freeze; I wouldn't feel comfortable spraying the world with anti-freeze, after all. Not to argue that we shouldn't use these, but that we shouldn't do things that make us have to use more of them.
Same with fluorinated waxes, which I love and have been using more and more. So far, their use is limited and so without huge impact on the world, but as the snow gets slushier more times of the year, we will be using more of them.