Now then, on Hail teams, Ice types are by far worth it. Now, let's look at Ice types in general before moving to specific Ice types.
Ice types have an excellent attacking type. They are one of the few Pokemon to geta super-effective hit on Dragon types. Ice also pairs up well with attacks of multiple other types: Bug, Water, and Electric all work well with Ice.
Now onto specific Ice types.
Dewgong is first off, being the first Ice type in the Pokedex. Now then, Dewgong is great in the lower tiers. Its Rest+Hydration strategy makes it very difficult to KO Dewgong.
Cloyster has great moves and a great ability. Shell Smash doubles Attack, Special Attack, and Speed at the cost of a one stage decrease in Defense and Sp Def. Cloyster has a high base defense, so it might actually be able to take some hits after that. Then we go on to the other moves and the ability. Skill Link is amazing, making all of Cloyster's multiple hit attacks have technically base 125 power, with an added bonus of being able to break through Subs. Icicle Spear, Rock Blast, even Spike Cannon are now incredibly deadly.
Jynx is goo in the lower tiers, able to quickly put the foe to sleep with Lovely Kiss.
Lapras is one of the best Pokemon in my opinion. It can run either a Physical or Special set. On the Physical side it gets awesome moves ike Dragon Dance and Ice Sard. On the special side it gets attacks of higher base power (although no stat raiser) and Thunderbolt. Lapras is also bulky and has a great ability in Water Absorb. Thunderbolt allows it to be perfect as a Water type counter.
Glalie gets an awesome ability called Moody. While unpredictable, this can potentialy make Glalie incredibly powerful, and it actually works great with those evened out stats.
Walrein is famous for being able to survive for 32 turns on a Hail team. It is a great staller.
Regice is a defensive and offensive behemoth. It works great on a Gravity team with Blizzard and Zap Cannon.
Abomasnow sets up Hail.
Weavile is a nice lead, what with Fake Out and all. It has a great attack and a great speed stat.
Glaceon has a high special attack. In Hail where it can't be hit, t can cause a ton of damage with Blizzard.
Mamoswine has an awesome attack stat and STAB on two of the best attacking types. In Hail it is even more powerful, as it can't be hit. It also gets Ice Shard.
Froslass is great for setting up Spikes, then taking the foe down with it with Destiny Bond.
Frost Rotom gets Electric and Ice STAB, which is a great type combination.
Vanilluxe is an excellent sweeper with a Choice Scarf, going off of a high Special Attack stat.
Beartic is great on a Rain Dance team due to Swift Swim. It has an excellent number of physical moves like Superpower to bolster a good Attack stat.
Cryogonal is just plain awesome. Words cannot explain its power.