I use the Dollar Tree figures, since they're close enough for O scale and that's what I have. The buildings are undersize for O; they look closer to HO to me but I didn't measure them with a scale ruler. I could see using them in the background for some forced perspective on a Christmas layout using O scale trains. I use the lights; they're close enough for me, they look good, and the price is much better than the Model Power lights intended for the purpose.
If the buildings are a bit off for HO, you might use them anyway. Christmas villages all have quite a bit of variance in them, as they're going after looks and charm, rather than accuracy. Keep scale pieces--figures, automobiles, etc.--far enough away from off-scale pieces to keep them from giving it away. Creative use of forced perspective can create the illusion of scale even where there is none. And the Dollar Tree buildings are cheap enough that you can build a very impressive-looking village for your layout for very little cash.