Those services could easily be honeypots for collecting information... PGP encryption is safe on a non-internet connected machine, in theory.
Yes, it's safe. Never install PGP on a desktop/laptop that you use to surf the Internet, ESPECIALLY when you're logged into your administrator account.
Having PGP encryption on a non-internet connected machine, will protect you from compromise for the following reasons...
(1) PGP keys can't be stolen. Save your PGP keys on a thumb drive, NOT the hard drive.
(2) PGP software can't be compromised with man-in-the-middle spyware.
(3) Encrypting text in the PGP crypt-text format, and then saving on a thumb drive, to send over the Internet via a internet connected machine - WILL ENSURE absolute encryption at all times.