“Summoning” Undead is actually going to work a couple of different ways. Some spells create undead rather than summoning them. You can create skeletons or zombies out of available materials. If those materials aren't available you can summon them from the shadow plane. Incorporeal beings always have to be summoned. You don't really “make” a wraith. You summon one. So, it really depends on the circumstance.

I'm afraid giving base units “officers” would make them too powerful and/or too expensive. It's an interesting idea, however, and you will see undead units like Huecuva able to bolster other undead on the battlefield.

I do see the point about the engineer... We have to think about it...

Bone storm is unique, but it might be a little too unique for the average taste. It's one of the things we might put to a vote.