We sometimes have a Loyaler game on Full Tilt for the long-serving members of Cardschat. The players know each other very well through the forums, and many of us have also met each other in real life.
FT have no objection to that. The things which are objectionable are soft-playing or chip-dumping to a friend, or colluding. If you play tough against your friend and make every effort to beat him, just as you would any other opponent, it is highly unlikely that any questions will be asked.