[Mightypeon]

Some random impression:

A full scale build can work, although Ulm still can benefit much from Nature.
Ulm is guaranteed Death Access at Construction 6. Also, this death access has a forge bonus of 35, gets occasional Nature picks and autocasts Gaias Bless (resistance to all elements) in battle. The spell you are looking for is icon of the forge. Since they can forge Fire Skulls very cheaply, they get you into Fire.
Ulm gets 2 special summonable commanders that cast relief or mass luck respecitivly. These are incredibly powerfull together with an army.
Ulm can summon Black Guard equivalents for 1 Earth Gem each. To do so is quite economical in terms of Mage time. Any Priest Smith, or Black Smith with Earth Boots can do so.

Enchantment gets Ulmish Black Rose Priest, that autocast fury. Unfortunatly, it means that your mages may also run up to the enemy, so it is a bit of a niche use.
There is also the radiant standart, a tough fighter auto casting Solar Brilliance. Those 2 should perhaps not be used with a large army, but rather be seen as an IED device.
Enchantment also has the possibility to recruit Slayers. Slayers are Black Guard but have Flambeus instead of Black halbers, and have Morale 30.
To cast this spell, a Priest Smith or a Black priest with an F random is needed.
The last of Ulms special troop summons is perhaps the most powerfull, but costs S gems which Ulm will likely use for other things.

I can only recommend trying Black Rose Ulms special pretender, as long as you dont take him imprisoned, you will soon have more spies than you can use, as well as a cadre of assassins. Those assasins are sacred, autobless themselfs and carry one handed hero blades, making them quite good for assasinating giant nations, or everyone on a horse.