The hash method would be Vanilla not phppass. phppass is lower level but not used to select the hash method. Blowfish encryption is sometime used by phppass and this can affect portability. If you are using SSO then just go with that.
I think it will still be completable with the phppass passwords, as that would be needed for update. So Vanilla should work has the hash method so long as internally the phppass options are transportable. However I agree if using SSO, you don't need to worry about Password authentication.