How can you even effectively play the Demoness when half of the classic Order spells will be USELESS? Resurrect, Bless, Heal and all these now don't work on "Of the Dark" units, and 100% of your army will be composed of those. And they have no "reverse" spells of these. Worse yet, this means the enemy can use their Priests to attack even your orcs and demons, when previously they could only do it to the undead.

After you acquire a mage named Simon at your 'shelter', you give him 3 of those type spell scrolls and he automatically converts them into Dark Side versions and automatically puts them into your spellbook.

Even Resurrection.

The best healer I've found for the Dark Side to use is the Demonologist and pair it with the spell Phantom. Also, Alchemists(dark side chemists) can even heal your Magic resistant creatures with it's "healing bottle". I use that one for my Dragon Riders as they're too expensive to let even one die,lol.

After you complete Portland, Dark Side "Traitor humans" become available at the castle and every store. Priests become Heretics and inquisitors become Hereticarchs. These will do until you get the demonologist and alchemists.

Poison Cloud and Call to Nature are very good spells to use in this version. Call to Nature especially with the Demoness' high leadership.

I had no problem with restroing my armies. At first i was toying with sacrifice from demonic priestess, it was kinda awkward but worked. ON portland dark paladnis + heresiarch(heresiarch are kinda limited in the game like inquisitors in legend, but i used sacrifice to rise the numbers). The spell which gives paladin 4 charges ( creation or something liek that) to his ress is just ridcoulous .NO more need for endless phantoming.
Besides as said above u can have resurection working on demons via school of magi in shelter..