Sure, I'd take a mistress over a hound any day of the week, but mistresses are just damn good. Skeletons aren't that much worse than hounds, but they will lose in a straight up fight. The skeletons redeeming feature is their lightning, which they only get at lvl 10, where the hell hound gets his must powerful spell - speed - at lvl 3 already.
And I find skeletons to be much more annoying as well, not just because of them being lair enemies to the much appreciated but gassy biles, but most of them that they will fill up my training room even when I don't want to on low-gold maps. There I'd want to get my mistresses trained, or my vampires the first few levels and keep the rest of the gold for the next payday.

It's just a shame he always comes so late in the game. That's the main reason he will hardly get any use, even if you haven't already won or at least explored the map by the time you get the scavenger room, by that time you do you often already have trained biles, mistresses, dragons and orcs, perhaps even reapers or vampires, so you're not really waiting for a mid-tier unit that's especially useful in exploring the map.