I think the frets on "fretted" violins (other than viols de jamba...er..."leg viols" from pre-violin days) are more like the lines on a fretless bass. I've never seen one in person, but they have to be either flush or damn close to flush with the fingerboard. Otherwise, there's no way you're getting a finger in between some of those upper frets. They might just serve as visual markers.
My teacher used to use electrical tape cut into itty bitty strips for that. White-out also works if you have a steady hand, and it wears off the wood over time. So as you get good at placing your fingers, your visual aid disappears.
Mandolins are somewhere in the ballpark of a violin and a 12-string guitar having unnatural inter-instrument-family relations. 8 strings, strung like a violin, fretted like a guitar, strummed like a guitar, sounds like someone plucking two violins in sync.