In the monster entry for ghouls they have a paralysis ability. This is applied to both their claws, and their bite, which makes me believe this effect is applied on touch. Similarly the spell Ghoul's Touch seems to lead me to believe that it is in fact a touch effect. Is there anything that states one way or another? Could a ghoul forgo the claw (or bite as it does not seem to be tied to their claws) attack to try to paralyze as a touch attack?
A ghoul's paralysis is based on their bite and claw attacks only. The Paralyze special ability requires a specific location for it to work:
This special attack renders the victim immobile. Paralyzed creatures cannot move, speak, or take any physical actions. The creature is rooted to the spot, frozen and helpless. (...)
Format: paralysis (1d4 rounds, DC 18); Location: Special Attacks and individual attacks.
Since it requires a specific local to work, some creatures may only paralyze with one of their attacks, but not with the others. The Mohrg is an example of a creature that has touch as the location for their paralyzing special attack.
Melee 2 slams +15 (2d8+5 plus grab), tongue +10 melee touch (paralysis)
Special Attacks create spawn, paralysis (1d4 minutes, DC 21)
Only a mohrg's tongue attack can paralyze creatures, but not their slam attacks.
Even the dumbest of ghouls would simply try to grapple their victim before they start chewing on them if a mere touch could paralyze. I mean, wouldn't you, if you were a ghoul?
Classic Horrors Revisited (page 30) goes further to clarify this:
Beyond its hunger and the virulent disease it can inf lict on the living, one other quality defines the dangers a ghoul presents: its paralytic touch. Mere touch is not enough to visit this doom on a foe, the ghoul must pierce f lesh with tooth or claw and actually inf lict damage before the paralysis can seize the victim’s body.