(H)L makes this call alone. U isn't moving up to line of scrimmage on a punt play.

Umpire

1. Count offensive team players, knowing the ineligibles.
2. Observe defensive man over center. (Avoid serious injury to the snapper.)
3. At the snap. step forward to the line of scrimmage.
4. Be alert for runs and passes; assist in covering short or blocked kicks.
5. Following the kick after the players go past your position, and on a signal from the Referee, turn and move towards the return areas, with particular attention to clips or illegal blocks or other fouls away from the ball.

I'm not sure where you're getting these mechanics from, but why would the umpire want to limit his scope of vision of action at the line by stepping to the LOS at the snap? Stay back and watch for holds, illegal blocks, etc.

Once the players start clearing out, turn to watch the action of players going down to cover the punt.

Perhaps this is only a MN mechanic but on punt situations in 5 man we have the U in the backfield with the kicker opposite the R.

who is watching roughing the snapper?

...Probably the umpire

From what I understand, Pennsylvania writes their own mechanics manual and this must be a PA mechanic. I am sure if I am wrong, somebody will correct me.

Correct.

They only have that asinine 6 man manual that is home made. Everything else is NFHS I believe