This is just my understanding, not supported by tech documentation: it is not the CONTACT with some material that is a problem. It is that the entire tub needs to be able to move/expand/contract with heat etc, and restricting part of it stretches the bond.
In any event, I have done plenty with no known issues. I would contact American Standard and see what they say. If they do say to send in the foam, be sure to use the "blue" can, minimal expansion type. But don't do anything until they tell you what to do.