Glamour + stealth => +25 to stealth. They usually accompany each other. In vanilla, 60/67 units with Glamour also have stealth.
Themes like fae are intended to offset the lack of clockworks, crossbows, and such on lower-tech hoburgs, and so is stealth. The more technologically advanced your hoburgs are, the less familiar they are with the idea of subtly. Feral and agrarian tech levels have stealthy troops, while advanced and industrial do not.
Uganwald was agrarian, so most of our troops (well, none of our cap-only colossi, and none of our cavalry, and none of our "heavy" infantry with scale cuirasses - but still) ended up being stealthy. Our missiles were blowpipes, our weapons were bronze, and our armor was mostly leather, but at least we were stealthy! ... ... ... Yeah, everyone else was at least "advanced" tech-wise, so we really did have an unfair advantage going into the "worst troops on the map" competition.
Obmar was the highest tech level (industrial) but against the odds was also fae. This is a very unlikely outcome, and frankly it seems like a kinda painful one. Fae categorically prevents clockwork units (and makes crossbows much less likely), so you missed out on standard benefits of a high techlevel, but industrial categorically prevents stealthy units. So the end result was noisy, glamorous, over-civilized hoburgs galumphing around with plate armor, halberds, and such. However, I'm really not sure I want to make it possible for advanced and industrial fae hoburgs to be stealthy. There really is a beautiful awfulness to the current state of that extremely unlikely and horribly awkward combination of themes...
I suppose I could add a low-probability stealth pose - maybe ranged-only for ranger types? - in the higher tech levels. I'll give it some thought.