When I first started bowling that was how. I bowled. Back then though I don't think it really mattered much. Probably still doesn't if you are throwing a plastic ball with a pancake core.
That being said with the current bowling technology, If the backup ball is your natural shot, and you plan on sticking with it. Then yes have the PSO drill it. So that a lefty like me could pick up your ball and bowl with it. Not that you want anyone else using your ball, but you know what I mean. Having the ball drilled as if you were a lefty. Will only help maximize your backup shot.
I actually have toyed with having one ball drilled for a right hander just for the 4 and 7 pins. I can't justify buying a ball just for those two pins in my own mind though.😃