Endpoint Encryption

PGP Desktop Email can be decrypted with GnuPG?

PGP and GnuPG both follow the OpenPGP Standards.  Basic encryption and decryption between each other (provided its a more recent PGP version) will work

I would also agree that the two are generally compatible.  Sometimes, one will implement a new standard, or option, before the other that might cause temporary problems.  I don't think it is currently a problem, but there was a while when a gpg encrypted file was not being decrypted by PGP unless you first changed its file extension from gpg to pgp.