D.va’s movement speed comparison

No, D.Va's ultimate will not damage her teammates.

In general, no abilities can deal damage to teammates. The only direct way to kill a teammate is to do something that pushes them of the map.

If you see the 'TEAM KILL' notification in the center of your screen, that is actually to denote that your team has wiped the enemy team, not that you've killed a teammate.

In the case of Reinhardt's shield, it can block any damage (except for Symmetra's moves, Winston's gun, Junkrat's Rip Tire, his own Fire Strike ability, and Hanzo's Spirit Dragon) as long as it has at least 1HP. So a 1HP Reinhardt Shield can take the full 1000 Damage of D.Va's explosion.

Situation 1: McCree's lock-on delay for each player is increased proportional to the amount of effective health gained through Lucio's ult. Given that McCree is allowed to use his ult unhindered, you are correct in your assumption that Lucio's ult would do very little.

That said, the delay caused by Sound Barrier is likely to afford your team the time to either prevent him from going through with it or at least to find suitable cover.

Situation 2: It is exactly as you have said. In my experience, and as indicated by a player's account of his experience in this reddit post, increasing a player's effective health removes McCree's lock on effect; however, I am not sure if this resets the delay entirely or if it just increases the delay proportional to the health gained. Either way, it's worth investigation.

In short, Lucio's ult is very effective at countering Deadeye.