Now that I've faced more Imperial Guard stuff, I've had more time to reflect on the units.
In essence, the guard can get stuff that's roughly equivalent to the Space Marine's Multi-melta/Heavy Flamer landspeeder. Now, why is the speeder actually something we want? The marine speeder mounts one of the best anti-tank weapons (the multi-melta) and a superb anti-infantry weapon (the heavy flamer).
Additionally, the landspeeder can use its speed to get into position. It can move 12" and fire one of the guns. Now, immoblizing a speeder hurts because the flamer's all but useless. Still, the melta's an issue.
So, after some thought....no, the Hellhound family CAN get this. It's also on a 12/12/10 chassis that, admittedly, doesn't get the simmer bonus of hopping over things.
So, we've got three types of guns on the chassis.
The Hellhound: the big advantage here is that the flamer can project. It's effectively a heavy flamer that can reach out a bit. It can also take a hull-mounted multi-melta. Now, an immobilized result is inconvenient, but the Hound at least creates a death-zone around it with the flamer for infantry.
The Devil Dog: At first glance, the melta cannon looks a bit 'eh'. It's a multi-melta blast, which means "Oh, I rolled a '12' on the scatter' and wasted the shot. When you get down to it, it hits on the 'hit' 33% of the time, and will probably hit around 50% of the time anyway when you deal with scattering.
However, if you fire it at something OTHER than a vehicle...it's basically an S8 plasma cannon. It nukes armored infantry; power armor is no protection. It'll insta-gib T4 folks as a bonus. It'll never Get Hot. However, there's still the cover save to deal with.
Then, you can compliment it with a heavy flamer, and you've a more expensive, but still disgustingly capable tank.
The Banewolf: S1, AP3, wound-on-2+ flamer? It's the death of expensive units like marines, terminators, and Wraithguard. The real question you have to ask with the Banewolf is whether or not you want that extra punch over the heavy flamer.
It's a tough choice among the three. The Hellhound has the most range of the group, so suffers the least from an immobilized result. The Devil Dog has the most disgusting ranged weapon and the best range on it, since its melta cannon pulls extra duty as a plasma-cannon stand-in. The Banewolf packs the most deadly flamer, but you only get that extra oomph against certain targets. It burns regular infantry just as well, but only really makes its points back against marines and terminators.
Ultimately, some of it will come down to the overall army composition.
The Valkyrie family
More, the Vendetta. A Vendetta with heavy bolters is going to scare anything on the field, and for 10 more points, the heavy bolters aren't that bad. They ARE wasted against most armor, but if you're hunting AV10/11 (like Rhinos, Predator flanks, Chimera flanks, and so on...) it's more pain to bring.
The Vendetta, though, really seems to shine as a hunter of monstrous creatures. Given the height and angle of the Vendetta's guns, there's really nowhere to hide. A single Vendetta should get 2-3 hits a turn, and since those'll wound on a 2+ most of the time, well...that's 2-3 wounds off an MC. Soften it up and finish it with a Vendetta, or put two on one and watch it die. Add in the heavy bolters and they might knock off a wound more.
For 140 points, it's not a bad transport. I'm somewhat tempted to do a Guard list with inquisitorial allies to justify running Vendettas and Valks.
I haven't seen a Valkyrie in action as much. At best they'll be swift infantry hunters, with a milti-laser and pair of the S4, AP6 large blast missile pods. They get to move 12", crank all their shots off, AND carry a squad.
Then again, the Guard can get a LOT of capabilities in their slots, and versatility Even a short look says we can get infantry hunting, tank-hunting, or both in any given fast attack slot.