I'm not aware of any cross compatibility in the sense of disks orignally encrypted by PGP being accessible to machines running SEE. The only compatiblity I can think of, is the abilty to upgrade from PGP to SEE.
That said, it's unclear what form of encryption you're talking about here. Is it the EOL PGP portable, a PGP self-decrypting archive, a FileShare Encrypted file, or a WDE encrypted external disk?
If either of the former 2, any machine should be able to access the data without installing any software, so haing PGP or SEE is not really a factor. If either of the latter 2, I do not believe a machine installed with SEE will be able to open the encrypted resource (file or disk, respectively).
Does this help? What's your use case?