[thejeff]

I haven't tested the skelly trinket spamming commander and guards, but what I would expect is this:
He and his guards would not count as troops to stay behind. No commanders or bodyguards do.
But, the trick might work anyway. Commanders on "Stay behind troops" try to stay behind the rearmost troop on the field. The most recent skeleton to appear would count.
I've never tried to exploit this, but I've seen it with skelly-spamming mages. Later in the battle after the mage exhausts himself and recovers to cast one more Raise Dead, I've seen commanders turn from the rear of the main line and race back to behind the new Soulless and then follow them forward.