I was already looking into a solution for this myself. It has to do with the recalculation of the snow height for Extreme Hills biomes. My Bug, My issue.

Is the snow also supposed to be generating in smooth tile-based layers on the mountains?

Your question doesn't have any relevance to this issue, so I don't know why you are asking this here.

If what you are refering to is happening in biomes that generate those layers (ice plains), then yes. Sometimes flatter biomes have poor transitions into mountainous ones and ride up into mountains.

Nothing can be done about this without completely rewring the terrain gen system in RTG.