Would you mind elaborating this please?
The thing about fire attacks is that Abomasnow cannot afford to take them at all. Not to mention that the prevalence of steels in the Metagame means that they are everywhere, not limited to Stab-ed users such as the ones you have pointed out. Victini is also another dangerous sun abuser.
Magnezone, Celebi, Genesect (especially with +1 SpA), Tornadus-T etc etc.
I suppose the shitty fire weakness is due to the fact that all other weather teams have an innate resistance to them - save 'Tar who hates burn. So that's a slot you do not have to worry about. Whereas for hail, that's an entirely different story.
Coming back to Infernape, any opponent worth his weight will notice that Heatran is your fire check and throw out a CC, which, by the way, also hits Abomasnow and Kyurem for SE damage. It's a bad scenario when more than half of your team is weak to one of Nape's moves. IMO, 'Nape is number one on my checklist when making a hail team. It even has Stone Edge to cripple Draognite/Salamence, and although not seen often, can run Earthquake!
Yeah, Ape is probably the biggest threat to Hail, which is why I tend to run 2 solid checks and maybe a 3rd that can work in a pinch.
I was never trying to say Hail didn't have a Fire-type weakness, but I wanted to make clear that adding another Pokemon with a Fire-type weakness (Like Scizor) doesn't cripple your team, since you should have solid checks to Fire-types and Pokemon that run Fire-type attacks anyway. I don't think we're disagreeing an anything, since I didn't make my point clear, but I what I mean was that I don't find Fire attacks that debilitating to a Hail team when resists and counters are not difficult to fit onto a team. For example, I'm currently running Tentacruel (Probably the best Ape counter in the game) and Heatran, and they fit easily onto my team and provide support far beyond taking Fire-attacks. Any Hail team that actually worries about Fire attacks needs work, just like ANY team that worries about Fire attacks needs work.
Anyway, what I was saying about all Hail teams running a solid Fighting-type... There are no absolutes, but Fighting-types have such great synergy with Hail teams that there's no real reason NOT to run one. First of all, Fighting-types provide an instant Rock-resist and also automatically resist Tyranitar's STABs while OHKOing or at least doing massive damage with their own STABs. Fighting-types also provide a way of breaking through Steel-types, and each Fighting-type I listed provides support in its own way. I'll go into a little bit of detail on each:
Machamp/Conkeldurr: They are incredibly similar Pokemon, so I'm listing them as one. They both provide a bulky, hard-hitting Fighting-type that can counter Tyranitar easily. Conkeldurr is probably the better option in many ways, with Mach Punch and a good Bulk Up set or a Guts-abuse set. But Machamp has interesting support options, like Encore, which can get another Pokemon in. Unfortunately, Machamp's amazing Substitute set doesn't work well on Hail teams with the lack of Leftovers recovery.
Hariyama: A Tyranitar counter AND a Fire-resist in one with Thick Fat. Whirlwind for phazing is icing on the cake. The only reason Hariyama isn't used more often is because he's more of a niche Pokemon than Conkeldurr or Machamp, but he fills that niche perfectly on Hail teams.
Hitmontop: With decent physical bulk thanks to Intimidate, Hitmontop has a unique place on Hail teams with the ability to Rapid Spin. Foresight guarantees a Spin, and an offensive Spinning set with Technician can revenge things like Terrakion, DDtar and Alakazam with Fake Out and Mach Punch/Sucker Punch.
Gallade: Gallade doesn't really provide team support like the others, although he can run a decent double-status set with T-Wave and WoW. But he does provide a Specially-bulky Fighting-type that can sweep pretty well with a Bulk Up set. Like Hariyama, he's a niche Pokemon, but his niche is present on Hail teams.
Look at the Hail teams in the RMT section. Almost every successful Hail team runs a Fighting-type. Delko's Christmas team in the archive runs Conkeldurr. Jubilee's UU Hail team ran Hitmontop. Every Hail team I've ever built that's worth anything has run a Fighting-type, and I've built several. Yes, admittedly it's not a requirement, as some good Hail teams have gotten away without running one (JabbaHail and the Glacial Cataclysm team on the PO Youtube channel), but both of those teams were focused on hitting hard quickly as opposed to trying to take hits. Fighting-types just naturally compliment Hail teams.