[Bruno]

Soldiers are not Allies. Soldiers are employees - player characters and non-player characters can just hire people and pay them money and deal with loyalty. If you treat your evil army poorly this may result in desertion problems so overall a lot of time and resources will get wasted stopping that and/or kidnapping new recruits, but they're still just employees. You pay for Rank to have a lot of employees you can command, usually, not bulk Ally Group.

The Presidents/Emperors/Overlords Guard might be Allies... unless they're actually more loyal to the Army than they are to you...

An army of skeletons and zombies may not count as Allies. If you can't control them directly, you instead pass orders to generals who pass orders to majors who etc etc. I wouldn't call them Allies. You will have the same sort of communications problems and problems with following orders as real armies, although the logistics will be a lot easier. They probably won't desert, but they might wander off (or rot to pieces).

Of course, if the Evil Overlord controls their vast skeleton army personally and they respond perfectly to his commands, that's a lot like an Ally Group.