I swear, Sub / TWave / Spikes / Ice Beam Froslass in hail is one of the silliest things in the metagame. It has its counters, but it's also ridiculously annoying, not to mention effective. I'll probably nominate Snow Cloak for next round, and with it probably Sand Veil too.
I've yet to try Chansey on a more balanced team. Problem is it doesn't offer much. It's easy to get set up on, and a Pokemon behind a sub is difficult for an offensive team to weather without losses. It can't put up entry hazards either without losing a precious move (e.g. Wish without Protect), and it'll always be vulnerable to the types it doesn't have a status move for. I can't see it working alone, and I can't think of a good partner for it in a 2-man core either. I guess Slowbro is about as good a partner as it gets, but there're still Pokemon like Heracross who just go straight through ...
The problem set for me seems to be:
Sub/T-Wave/Blizzard/Coverage
You wouldn't be running Sub + T-Wave Froslass unless it was in the hail anyway.
On an addittional note, banning Snow Cloak would soft-ban Froslass, who is basically the main issue. Glaceon and Mamoswine are not, they can't abuse Paralysis, and are also both slow. Glaceon lacks a movepool, and Mamoswine can't abuse Blizzard.
In all honesty, a Snow Cloak ban would be rather pointless. The problem is like with Sand Veil and Garchomp, it lies with Froslass.
Which is also incredibly effective outside of Hail as well. Although, people seem more prepared for my TrickSpecs Froslass now...
Hell, despite a limited movepool, Froslass can:
Abuse Hail, with Sub/T-Wave/Blizzard and Snow Cloak
Use both Choice Scarf and Specs with brilliant efficency, and can trick both
Lay Spikes with relative ease
Using it's Base 115 Speed, also known as, I outspeed virtually everything, it can take down something with it with Destiny Bond.
It has a rather nasty LO set with Ice Beam, Shadow Ball, Hidden Power [Fighting], and a filler, possibly Destiny Bond.
Seriously, I'm starting to think Froslass might be the suspect... especially if Chansey goes. [Who can wall Froslass all day long]