you need to get the passport, if he gets one
then it is a crap shoot
if they check, which is about 15% chance, then he may be let in because of the type of visit or they may denied entry.
it sure screws up the trip if he's sent packing...
it happened to us going into the US, my buddy had history that I didn't know about, they would let me go but he could not enter, so I turned around and went home.....sure was an expensive 6 hour vacation