When cooking pulled pork in a slow cooker, should the meat be submerged in liquid?
For pulled pork, there is good reason to only use a small amount of liquid. Use only enough liquid to come nearly half way up the side of the pork. 

The pork that is sticking out of the liquid will brown, much like a sear. The mechanism is different, but result is the same. The exposed meat will develop color and that extra meaty flavor that gives good BBQ its character.

Since you're planning on an 8-10 hour cook, you can flip the meat halfway through to get that effect all around.

Flavor your added liquid generously, and be prepared to de-fat it when the pork is done, it will make for a great sauce.