They do not get the feat for two reasons.1) Dwarven Weapon Proficiency only makes martial dwarf weapons simple for the purposes of determining proficiency.
2) Warhammers are not dwarf weapons, so Dwarven Weapon Proficiency does not make them simple weapons. A dwarf weapon is a weapon with the Dwarf trait, which at this point are only of the clan dagger and dwarven war axe.
And.. that was fast! Thanks I figured if anything it would be because the weapon is martial to begin with and its d8. Seems it is only there to pump d4 and d6 damage types up. But your other reasons make sense more then the fact of the weapon being martial initially be the deity. And looking back it only says you are trained in those weapons looking further down makes sense. Thank you!