Assuming it can survive a round (because if there's one thing dragons aren't automatic winners at, it's initiative), a Huge or larger dragon (which we're dealing with here) with even a modicum of sense will just Snatch the poor lone sap attacking it and breath on it every so often (no save) until it dies to death, assuming it can find it. The Adept doesn't have to go it alone and can take measures to reduce being grabbed, so I'm putting my money on the Adept since it at least forces the dragon to move to Plan B.
The monk is going to auto-lose the grapple, basically, because high-strength, huge enemy with obnoxious BAB. Do monks have abundant step yet? If so, the monk can escape by wasting its turn, then get Snatched again. If not, it can rely on magic items that grant short-range teleportation that the Adept already has in addition to its other tactics.