I must confess that I have no idea what you are arguing here.  Are you arguing for, or against, tight punting formations?  I haven't a clue as to which scheme Michigan or Purdue uses, and the Alabama example means nothing because there is no context or counter-example here.

...because it's supposed to be an argument against the NFL-style protection they use, but they were #1 in the country in net punting.

There might well be a cogent statistical argument to make in favor of shield-punts. This wasn't it.

Any special training or personnel needed for the spread punt formation, or is it something a team  can switch to whenever (before offseason practices start, obviously) they decide to?

Iowa 2003. Didn't work. /s

Would be nice if someone averaged the Yrd/Ret of all spread punt teams and all pro style. would be an interesting presser question if we had the data.

Clearly the best answer to the punting style question is to convert on 3rd down.

Shield (Called spread above and often called that, to everyone's confusion)

Strength: Long snapper mirrors, two OGs get spill, two ends still act as gunners, and OTs contain. Shield players and punter are safeties. It forces the defense to declare its intention. It gets more players down in the first wave. Is more spread out (similar to a KO) and therefore is easier to define coverage lanes. Simplified release for the players on the LOS (step outside into gap and release upfield instead of going back to block).

Weakness: 4 guys in the two A-gaps can block a punt directly up the middle (shortest route to the football); rushers are typically going up against OL and FBs in space for the "shield" aspect of it, and it's hard for those shield players not to chase. Besides the rugby scramble, it's also more difficult to fake because penetration is allowed. After the first wave you have less support because you have OL types chasing the play and acting as safeties. Punt generally needs to get off quicker and cleaner because block angle is shortest route to football and there is less emphasis on protection.

Spread (Pro-style)

Strength: Can pick up any 8-man rush, and forces rush to come from the outside (don't let anything inside of you). With more defenders covering the gunners, you can release different players at the snap and leverage the football. Can still use LBs, safeties, as wings and OTs if need be to get down field quicker in first wave. Protects against the block first. Learn an NFL style scheme (good for getting players to the NFL).

Weaknesses: First wave is essentially the gunners and maybe the long-snapper mirroring the returner. Tends to put up to four OL instead of three OL on the field. Isn't spread out and therefore is more difficult to get into coverage lanes.

Conclusion

The shield punt is better at getting the intial wave down field, meaning that it typically will limit return yardage. The issue comes if the coverage gets too spread out or out of their lane, and then the safeties are a few OL and a punter, meaning that it is dangerous if it can be blocked initially. It also means that a lack of discipline is a bit easier to exploit, because penetration is allowed and four guys in the A-gaps can't all be picked up.

Conversally, the pro-style punt forces the rush to come from the edges and can pick up 8 men rushing the punt without problem. The protection is simplified (rather than the release), meaning it's easier to prevent the block. However, the first wave is typically only two players. The return against this formation is more likely (brining in variability), however, the return yardage is typically less variable (because there are more waves).

What it comes down to, is that a shield punt is often kind of all or nothing. Your punter's distance may drop a little because he has to focus on punting in the direction of the shield and has to get it off quicker and cleaner; if he doesn't get adequate hang time, the returner must only break through the first wave and bust a long one, however, that first wave is larger. A shield punt is more conservative. Your variable comes in allowing a return more often, but there will be less drastic shifts in field position. 

So what you'll see is a lot of defensive minded coaches do the pro-style punt as it tends to give the defense a chance to get off the field, rather than saying they need more yards in order to do so. Offensive minded coaches think about winning some field position or getting the ball back quickly if they don't. It's really a mind set thing.

My feelings

In general, I prefer the shield punt myself. There's a reason you spread out on KOs, you might as well utilize that advantage on punting. I think blocked punts are a rare thing anyway, as are fakes, so my preference is the shield. But I see it both ways.

On a long punt that Hagerup booms downfield we are look at an average of 10 yards/return? So on the shorter punts coverage will get there quicker so that should be reduced correct?  I am not against the spread punt but I am just curious as to how Hoke seees it.  GIving up 10 yards in the other teams redzone area or even less than that on shorter punts doesn't seem like it matters that much, but I don't know jack.