The case here, is that one penalty is for multi-tasking or acting while distracted. The other is accounting for recoil. So arguably both should apply if one is both moving and affected by the laws of physics.

More important is the spirit of the game. I could argue for a few hours about how different guns should have varying recoil ratings and its also dependent of the shooter and their familiarity with the weapon. (ie, the M-16 is designed to be low impulse on the shooter, the M-14 had a big kick, and an M82A3 Barret can't/shouldn't be fired from an unsecured position.)

However, the point of the rule is that players can't just stand against the horde and score 3 head shots in a round until their numbers thin. If you want action heroes apply only one or neither, if you want to keep them on the run enforce both.

As pointed out before - missed bullets are a waste, and zombies don't fear suppressive fire.
There is a fine line between hobby and obsession. I seem to have lost sight of it some time ago.