Is that even with the such low Accuracy of Sheer Cold. I could imagine it being good if Suicune knew any lock-on moves. But to my knowledge, Suicune doesn't learn any which means Sheer Cold feels like its going to be a lucky-if-I-hit kind of move. I might not know everything about as I'm still getting into the competitive scene slowly.
The key is that this you only have to KO 3 opposing Pokemon to win, and the laws of probability dictate that even with 30% accuracy, if you sit there spamming Sheer Cold, you're bound to hit eventually.
Now, I'm not sure how well this would actually work, but here's a bit of theorymon for ways to counter the Big Bad Bulky Beasts (Suicune, Chansey, Suicune, Skarmory, Suicune, Snorlax, and Suicune).
Murkrow @ Eviolite
Ability: Prankster
Impish Nature
EVs: 252 HP / 252 Def / 4 SDef (Physical Defense investment is more viable due to the large number of Physical threats in the metagame)
-Mean Look
-Perish Song
-Protect
-Foul Play / Taunt / Torment / Roost
That's right, Perish Trap. It requires a bit of prediction in order to hit the fatmon with Mean Look on the switch-in, and then a bit of luck to not get hit with Sheer Cold, but the trick here is that Suicune will want to come in on Murkrow to Sheer Cold it or set up Calm Mind, so you can trap it with Mean Look, and then Perish Song and stall with Protect. The last slot is a bit of a toss-up; Foul Play is Murkrow's best way of dealing damage, and ensures that you're not Taunt bait, while Taunt and Torment can be used to stallbreak even more. Roost is good for staying healthy, though I'm not sure how useful it would be in the more fast-paced 3v3.
This could potentially also work to phaze setup sweepers.