Is there a regulation on that clarifies whether or not a Drop Leg Dump Pouch is allowed?

You need to ask that SSG to show you the reg. In my unit, guys could use whatever gear they want. Within reason of course. I don't know of any regulation that says what kind of gear can and can't be worn. He may possibly be talking about a unit SOP or something. But still, if he's making corrections based on a regulation, he should know the regulation.

Either it is or isn't in the regs- they should be able to show you it is. It might be against unit SOP, but again they have to be able to SHOW you. Normally in my units, if it worked well, and wasn't garish/outlandish, the CO would turn a blind eye in the field.

In my opinion, if a piece of gear makes the job easier to do, or enhances the execution of such...it should be allowed and even encouraged. However, if that piece of gear is just extra weight and bulk added for no good reason other than it "looks good"...it can start a trend towards "tacticool" that can impact discipline and efficiency-particularly if first adopted by someone in a leadership role. That's likely what the Staff Sergeant is thinking about...and if I were you, I'd play ball.

If you find yourself in a situation where you're truly concerned about expending multiple magazines and don't want to be dropping them all over the place...there are some less overt "dump pouches" that roll out of a compact holder, cost much less, and serve the purpose without making one look like a "Gear-do".