Yeah, I checked after my earlier post.
Full snow blocks, packed ice, and hardened clay do generate naturally, but only in those relatively rare biomes. But since (from my own experiences) I personally feel that a player would create and use those blocks (and want them to show up while xraying) far more often than they will be trying to x-ray in one of those rare biomes, it makes sense to leave them showing. They can always be easily turned off if the player enters one of those biomes.
Since players use this mod for many different reasons, and there is now the global auto-exclude option, it would make sense to keep the "blacklisted" blocks (when using auto-include) to the bare minimum. IMHO, of course.