It would make sense.....
I mean, since I was a child, I ALWAYS knew that Pirates had Treasures and Treasure Maps....
AND, they were hell of a Treasure, also, not just a few pennies, but lots and lots of nice and good stuff which they had collected over the course of their, aheam, "career".....
It would only make sense to see Trove Treasure Maps, or at the very least, Hoard Treasure Maps on Dread Pirates....
With the nice variation, from time to time, to be able to get an Nice Ancient SOS from a Dread Pirate in place of a Treasure Map.....
Yup that's how I read it. I even got a few off chests there for a while in the beginning. But it has ether stopped or the rate of drop is so tight that to get one you have to be super lucky and doing the right map.
I can almost guarantee that if you did get maps from them, (no i'm not calling you out, I can only take your word for it) then you are the only person to have ever gotten a tmap from a dread pirate, either in their corpse or in the hold.
Then you two are the luckiest UO players on the planet. I've personally scuttled almost 10,000 dread ships , I've never gotten a single one and i've been doing High Seas since it launched.