On the Umbreon issue: firstly, it sucks at Curse sweeping. Frankly. It's much better to use BU Scrafty, who has a Fighting STAB to work with. Secondly, it sucks at walling. Ferrothorn's only downside is an additional Fire weakness, but in exchange it gets broken shit like Leech Seed, Power Whip, Gyro Ball, SR, Spikes, Iron Barbs, Toxic immunity, and a crapload of resistances. It also doesn't warrant usage over Blissey on special walling. Finally, Baton Pass. whoops, trap pass got mega-nerfed, now BP doesn't pass Mean Look. In addition, Umbreon can't pass Quiver Dance or Shell Smash. And it still doesn't warrant usage over Vaporeon, who is like 100x better due to better STAB, better ability, and better HP to pass for Wish.
Since Umbreon sucks at everything compared to everyone else, I don't see how its going to be able to secure a place in OU :/
As for Chansey, here's one word of advice to Virizion: play UU. You'll be surprised at how bulky Chansey can be, and its near-impossible to KO without resorting to Victini or Close Combat. Chansey just needs Wish, Protect, Seismic Toss, Stealth Rock, Toxic, Thunder Wave and Softboiled. Really. It's the same theory as Excadrill, as to how it only needs like 4 out of SD, Return, X-Scissor, EQ, Rock Slide and BB, occasionally Rapid Spin. Or Breloom, who pretty much just needs Spore, Sub and Focus Punch to fuck shit up.