If SCAA only addresses POKEY at $4000 than I think that will be an issue. I don't believe the XM is currently setup to map POKEY to $4000. It's always been recommended to use $0450 for XM compatibility. I think it's theoretically possible to implement, but would mean adding code to the BIOS to identify the inserted cart is a SCAA, and adding a feature to the CPLD to allow the POKEY to be mapped to $4000 using one of the control registers. All possible, but we would need to discuss with Mark to confirm.
Regarding Froggie, I'm pretty sure it was programmed to work with POKEY at both $0450 and $4000. I tested a pre-release version years ago on an early XM and it worked well. Also, Beefdrop has been confirmed to work with the XM POKEY.