Good question. I put one of those O-rings with the rubber rings on it in a student silver plated headjoint about a year ago and so far no corroding of any kind. I didn't even think aboutthat. Interesting....

Note that "rubber" (at least in Spanish) is a general name for a wide range of materials.

It can have latex as the basic component, combined with many other products or it can be fully synthetic, long lasting materials that resemble natural rubber in some aspects but have a much superior performance (stability, neutrality towards other materials such as plating, and other physical parameters).

I can suppose that they have chosen the right material for those O rings. (yeah, I am optimistic today)