Thats a really good question! I dont believe they will sadly :/ It seems like i have a toon somewhere for which the pirate dlc levels got locked in low, because i went at the wrong time.
Now, do you still have the repeat quest open? After you complete and see credits, you have the exact same "Treasure of the Lost Sands" quest available one time for pick up in Oasis. If you've already picked it up, then i think you're out of luck :( But if you wait till 2.5 to grab it, it and the chests should scale :)
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I've actually started a Maya a few days ago. Did the treasure room as early as I could to farm it. I finished at level 17. My Maya is now level 22 and I just visited the treasure room and the rewards are still set at level 17. I'm pretty sure the rewards lock at whatever level you are when you finished it. This is on normal mode. Obviously 2.5 scales to you.