Well I made my own variation on this team, and it has worked out pretty damn well. Here are my suggestions based on my trials:
Go for Roar over Ice Fang. The only things Ice Fang hits hard are Salamence, Flygon, and Gliscor. The latter two are hardly ever seen, and Salamence is just as damaged by Roar with SR and SS going anyway. Having Roar as an anti-set up measure, and simply as a shuffler, is extremely beneficial.
There is no point im using HP Electric on Tentacruel. Who the hell doesn't use Earthquake on Gyarados? and with Toxic Blissey and Celebi, bulky waters (which dont take much from HP Elec anyway) are hardly a problem. Instead, I would go with Rest. Tentacruel is the only member of the team which cannot self-heal, and that, above other things, forces Blissey to use Wish + Protect. With Rest you allow Blissey to use Aromatherapy, which in turn allows you to clear sleep and other status from the rest of your team. In a metagame where a single turn of set-up can sweep 5/6 of your team, you really don't want to have that last member asleep or paralyzed or whatever. It's also incredibly useful when you don't have to care about Skarmory and Tentacruel being burned or paralyzed and you can just continue to lay entry hazards and then just bring in Blissey. So giving Tentacruel Rest and Blissey Aromatherapy and Softboiled over Wish and Protect allows this team to function better in the current metagame.
I used HP Fire on Celebi and it worked out OK, but I am not convinced it is the best option. It is pretty nice to eat those annoying Scizors who like to come in on GK, though (and to have a decent option against Luke!).
There is no way in hell that Spiritomb is better than Rotom. The only thing Spritomb has over Rotom is not being weak to Pursuit, but that pales in comparison to the fact that Rotom beats - not just stalls out - every spinner, and is a great counter to a number of other pokemon as well. Spiritomb is 2HKO'd by any reasonably powerful attack, despite its zero weaknesses. So a special defensive Rest / Talk Rotom is optimal here.