I personally prefer Tentacruel or Starmie, the latter more than the former. They both bring an excellent fighting resist to a hail team, while doing numbers against rain. I've had good success with both, but what makes Starmie just that little bit better is the instant recovery it has over the other spinners, plus it can check keldeo with psyshock. I've found forretress to be not that good for me spinner wise, but I guess I might be using it wrong.
The use of Walrein is a bit eh, everyone and their mother knows what set it runs and it isn't that hard to stop. Since Kyu B has been let down it has been a boon for hail teams, it can pull off a powerful mix set with blizzard or sub hone claws d tail set in hail to go with hazard stacking. While this may not push Hail over the edge and make it a rather dominant weather, it is a welcome addition. I also like to use Mamoswine in hail as my dragon killer, it works wonders, as well as against the therians. Lando T can also be used in Hail to be a good def pivot, a core I like to use is Sdef rachi and lando t, both cover opposite side of the spectrums and rachi provides wish support. Water attacks can be annoying, but abomasnow and starmie help with that. I've found hail to be an interesting weather altogether.