It should be, but I don't think polearms or axes are eligible for the Arcane Implement Proficiency feat. I wish they were though, I have a Barbarian/Warlock that would make his axe into an implement.
Well, if one was after the 'reach' aspect of the thing (because weapon damage isn't really as potent for a warlock), one could simply go with a glaive.
But, not so helpful for a dwarf.
That said, 'reach' is overrated for a warlock, particularily of the hexhammer variant. (which is what dwarven infernal warlock builds tend to be)
The idea of hex hammer is that you're relying on temporary hitpoints and the threat of being hit with Hellish Rebuke's damage rider to do massive damage.
Even if that's not the case, damage is your number one priority, and if you're seeking reach, well... you're a ranged attacker. You have more reach than a halbard could ever give you. And the halbard doesn't give you any sort of defensive option, unless you get Polearm Gamble later... which is sorta bad for warlocks anyways. Great for fighters. Bad for warlocks. And the one warlock power that cares about your halbard, Eldritch Strike... does less damage than Eldritch Blast with a halbard. Sure you can boost it with iron armbands of power, but you can boost Eldritch Blast with lower-leveled items far better.
So, assuming you don't want the halbard for your character concept (which trumps other concerns, imho), then if your idea is 'Dwarven Weapon Training', then you cannot go wrong with a Pact Hammer Mordenkrad + Eldritch Strike.
(By the time you can get Arcane Proficiency and DWT, you should be getting magic weapons. And Arcane Proficiency is useless for a warlock without DWT until you get magic implement/weapons anyways.)
2d6 brutal 1 + Constitution + 2 damage is pretty... damn... good. On top of that, you get access to Hammer Rhythm, which should be pretty easy for you at level 11 given your Constitution focus. All you need to do is start with Strength 14.
As well, this allows you to go with Chainmail armor. As a Dwarf, your intellegence will likely only start at first level at 14, so you'd be looking at an AC of 14 out of the gate. Even with your concealment, you're still only looking at equivalent AC of 16.
Granted, don't do it at level 1, you can go ahead and DWTSMASH your way to your first level up. But at level 2, Proficiency in Chainmail will pay off great dividends... raising your AC by +2 in the short term, and affording you the heavy armor progression in the long term. As a warlock in chain, you'll have the AC equivalent of plate. Just move 3 squares every turn.
You should do that anyways. Warlocks who stand in one spot are doing it wrong most the time.
