Meh, no idea. Still though, I find it awesome he fought with a warhammer.
I would say that the Reach has never had a really well defined weapon- longsword and shield (really traditional for a Knight), two-handed swords, spears, they're quite common. The Poleaxe is something they've probably adopted a little more, as a guardsman's/Retinue's weapon of choice- it's a pointy axe on a steel pole. Very Reach-like- if Dorne has it's spears, the North has it's fuck-off two handed swords that are almost unwieldy, then that might be the way.