??
Both my trailers have came with alloy wheels but a steel spare, with no separate lug nuts for the spare. So I've always assumed there's no difference.
The xtra tall lug nuts that were on the alloy wheel I replaced work fine on the steel spare so far. Drove across the continent with it. It's still on there and going to Florida soon. Recently had the trailer into a tire and suspension shop, and they didn't mention anything about it.
The conical shape of the lug nuts fills the hole you noticed. I torque both wheels to about 110.
On the other hand, lug nuts just for steel wheels may not be tall enough to fit in my alloys. But don't think there's any effective difference in threading or mating surface.