I wouldn't put that interpretation on either of those stories, personally. For the 10th plauge I believe the blood on the door was to notify the angel to pass over the house in question. Afterall the Angel of Death is not noted for being big on discrimination and may not have had any other way of differentiating hebrew from egyptian.
As for Lot's wife, simply looking at the angel may have been all it took. He may not have taken the feat that allows you to be selective with your gaze attacks.
So really it's more a matter of Angels not having a magic "Good Guy" sense that lets them instantly know sides, rather than having an agenda that may differ from the god they serve. Or in other words, they can't see those blue circles around the PC's feet.