The fourth stage of the "Van Kanighem" tournament.

What stealth level is required to complete the level with the "hide units" ability?

I had Grand Camouflage (level 5 stealth). This is at least what you need to get past the first Black Dragon outpost. But you don't need the "hide units" ability to get past this outpost. It's needed later. But regardless, Grand Camouflage is still required.