Compression test & leakdown test will both test the valves, in the sense of how well the valve seals against its seat when it's closed. That's not where oil comes from.

The oil seal around the valve stem can leak. That seal never sees pressure during either a compression or a leakdown test. On the intake valves it leaks the most when you shift, or when you coast with the clutch engaged & the throttle closed. That's when the vacuum is strongest, so it pulls oil thru the seal.