Finally, I get to join the legendary Smogon tier-talk!
I think Vaporeon is BL. It's a bit much for Underused, with a fair amount of support moves, good stats, and Wish. (Fake Tears is also a cool phaze move)
Abomasnow is UU. It's got many weaknesses (4x Fire is most crippling, but Fighting, Steel, Bug, Flying, hell even Poison!), meh stats, and all it does is set up Hail. Hail teams don't even work as well as Sandstreamers do in my opinion, since Ice is taken down by... lots.
Magmortar is poopy. Meh movepool, one good enough stat (Sp.Atk) with no Trait help isn't doing it for the red firebreather. It only really works on a Sunny Day team with Solarbeam and even then it's pretty meh. It straddles a fine line between BL and UU I believe.
I'm moderately disappointed that the most powerful attacker in not-Ubers, Medicham, is BL, but that's a discussion for another day.
First, Vaporeon is already listed as OU.
Auto-Hail is too powerful for UU, and is seriously, seriously unbalancing. Abomasnow's inclusion means nearly everyone will need to have a weather changer. It really burns a lot of strategies.
Use Magmortar before you spout about it. I've got an OU team that leads Magmortar that has a W-L record of about 52-10. Magmortar has a crap movepool? Yeah, Overheat, Thunderbolt, Thunderpunch, Mach Punch, Earthquake, Solarbeam, Psychic, Focus Punch, Focus Blast, Cross Chop, Flare Blitz, Lava Plume, Will-O-Wisp, and Rock Slide is a "meh" movepool. What do you want, Ice Beam and Grass Knot?
Magmortar has 95 Atk, 125 SA, and 83 Speed. That means it outspeeds nearly all of UU and can lay waste to a lot of them. Trust me, you let Magmortar into UU, and I'll twalk all over your teams with my Life Orb set, just to prove the point. Gastrodon and Quagsire are the only things that can switch into Magmortar. Everything else can be 1-2HKOd by one of its options.
Magmortar's defenses are 75/67/95. Awesome? not really. Decent? Yes.
Trust me, Magmortar may never be seen, but underestimate it at your peril.