Ronnie, unless I missed something, you appear to be right.
I looked in the rule book and did not see a rule requiring a fire suppressed padding for the seat.
Headrest padding needs to be SFI cert.
And yes, there are many things that, if ignited in a car, could burn.
Foam seat padding, potentially flammable types or others, is one of them.
But my question remains unanswered as well . . .
Why would you want to run with flammable foam under your arse?