I have polled the same question at another "room" that is access restricted. I was looking for cases. None could be found as to being used under foundations.
I have used the stuff under the basement floors of two houses that I have had built and no problems. Makes for a comfortable basement.
If you look at the crushing strength of the stuff and then go well below that pressure, it would seem it would work, but why be the first to do it?
I did that very thing for a cellar door area way wall foundations for my present house. So far so good, but we will see if the winter changes things. The purpose was to avoid going below that mystical thing called "frost depth".