basically you have an input pressure that is higher than the output pressure of the inline reg......as long as this is true it will work.
however the advantage of a high pressure reg would be that the input pressure would be a fair bit more than the output of the inline meening that it would have more chance to recharge under rapid fire.
with the lp reg it will work but if you rip off a long line of paint you may find that the velocity starts to drop after a few shots....you might get lucky tho if you reg can recharge fast enough