Onepocket.org addresses this question as follows:
Driving either the cue ball or an object ball off the table is a foul, whenever either comes to rest off the playing surface, or comes in contact with anything other than the table itself while airborne.
Note: In some areas, One Pocket has been traditionally played without a foul charged for jumping an object ball off the table, contrary to current general pocket billiards rules; therefore it is important to verify house rules or your tournament director's interpretation prior to an important match.
Ken