I might be wrong, but I think you are talking about a foam that is like that used in helmets and roll bar padding (relatively hard) and glen might be talking foam as used in regular seat or bed use (soft).
I could see where the "solid" type foam might be ok and even good in the type of racing that you are talking about, but maybe hard for the SCTA to inspect and feel comfortable about in our many different types of cars at this point.
It might be one of those things that if you provided a lot of documentation on how you were going to use it that might be considered, but that is merely a guess on my part.
c ya, Sum