How can I make my mouth less dry if I'm npo getting nutrition from a nj tube?

Swab the mouth. You can suck on ice chips, or someone can swab your mouth with a small wet sponge so your not parched. I dont think sucking on ice chips would be prohibited unless your stomach is completely not working. In which case, the water may accumulate and come up.
Suck on Olive pit. Try sucking on an olive pit a cherry pit or even a button. Anything in your mouth will stimulate saliva.