Undead elves make even less sense since only the Lich King has the power to raise non-humans, and why would the Lich King ally with the Horde in the first place? Sylvanas can only raise humans as Forsaken and only with the help of Val'kyr, which she has very few of. Her threat to raise Saurfang's son was an empty one as she doesn't have that power.
All of the undead rangers under Sylvanas' command were banshees raised by Arthas decades ago.
What gray zone of lore? The answer was crystal clear, and they do not need to say high elves specifically because blood elves ARE high elves.