I actually had a question about it, spawned from spending a long time EV Training in the Old Chateau and never seeing a Haunter or Gengar with FireRed plugged in... Are there requirements for the game used as a Dongle? Does it have to have been beaten?
I haven't found religion, but I have found FLCL. -ctriggercroneab Member of FAITH and Official GameFAQS Junk Tech
There are no requirements beyond having the gamepak in the DS slot, but Haunter is a rare encounter, and Gengar can only be found in one room (the small room with the moving eyes painting) and it's also quite rare.