I've used vinegar on some rusty impact sockets I picked up at a yard sale, and also on some old wrenches. It works, but doesn't really leave a good finish that you'd want to apply paint to.
That being said, if you want to soak those reflectors in vinegar, I don't think it would hurt the plastic at all, unless it is already weathered and porous. The plastic bucket I used is pretty stained with rust
I think you'd be happier with the results using the old fashioned way.
