It seems like this is sort of a newbie game, or rather, the majority of the people playing haven't been in the previous Bay 12 rounds, so you probably won't be overmatched. Anyway, the more the merrier!
Middle Age Ulm is pretty weak in vanilla Dominions. Their national troops are strong but not overly so when you compare them to some of the other human kingdoms. Man, Pythium, Ermor, Arcoscephale and T'ien Ch'i all have roughly equivalent heavy infantries and three of those of have cavalries that can basically match Ulm's as well.
Where Ulm really falls short is the lack of powerful mages, and the lower magic resistance of their troops (though the drain scales will help with that, inside their own Dominion). Sure, the Smiths have a forge bonus and the paths necessary to equip a few thugs, but they won't be able to bring to bear the powerful battlefield buffs and destructive magic that most other nations can wield.
