I have never used silicone spray, nor do I know anyone who has ever used silicone spray. My thoughts would be: use at your own risk - especially if oiling your valves isn't its original function.
In terms of damage, there are only a couple things to consider: Whether or not it will gum up your valves, and / or whether or not it is corrosive. If you find that it does/is neither of those things, then it shouldn't be a concern.
But please don't take my word for it - consult an instrument repair technician.
It doesn't take more than a few seconds to oil a trumpet's valves - I am guessing you're saving approximately 8 milliseconds by spraying instead.
Besides, couldn't you just put your valve oil in a cheap spray bottle and use that instead?
I have rotary valves, which are a lot more maintenance than piston. Be good to your instrument, and your instrument will be good to you.
Hope that helps.