Len said:
Yes, guards do look up. Guards with ranks in Spot especially - that's part of what Spot represents. As for night and dark clothes, those work on the ground too. And distance only works until he starts floating over the camp. (Remember, if they can't see him, he can't see his landing spot.)
Think of it this way: You're giving the character something like the Hide in Plain Sight ability, except better because he doesn't even have to attempt a Hide check! Doesn't sound fair to me.
Well, no - let's think about the illumination. The camp is presumably lit with torches and campfires, a mixture of direct and shadow illumination. The camp is also full of guards (people who are actually on watch and reasonably alert) and resting/sleeping soldiers (who might accidentally spot you, but who aren't actively looking). Assuming the target's in the middle of the place, sneaking in by actually hiding is going to be pretty tricky. You'll have to pass near guards or soldiers frequently.
Above 20 feet, there's nothing but shadow illumination. Above 40 feet, it's dark, unless there's moonlight or starlight. The KITE is in the dark, but that doesn't mean the landing zone is. Someone in the dark can see into the light just fine. Absolutely, the elevated approach makes avoiding being seen much easier. (Sure, you can't see anything in the air around you - it's dark. But it's the middle of the air. What're you going to run into? And you can see the ground just fine.)
Now, if there are any guards with low-light vision, that 40-foot range jumps up a bit, and the flying ninja is in trouble. If he gets spotted and someone puts a light on him, he's instant target practice for any spellcasters in the area. Not so much with the archers, if it's the middle of camp...all those arrows that miss have to come DOWN someplace, after all.
The real problem I see here is the NOISE. If there's enough wind to keep a kite like that aloft, you're going to hear the snapping of the canvas, the rope twisting, etc etc. And the darkness won't help you with that. And of course, there's the problem of getting back OUT.