I'm not sure if this has been mentioned before (if it has, I appologize), but I've read a little way into Frank Herbert's "Desstination: Void," and the parrallels are striking. The thing is a massive colony ship on it's way to Tau Ceti, with most of the crew in stasis, controlled by 3 AIs (sort-of...) whose design has a habit of going crazy.
The reason I mention this is, it offers a theory (supports an existing theory) on Durandal's shame, and why he'd be on the Marathon in the first place, and what the Battleroids are there for. If I understand correctly, the purpose of Herbert's colony ship isn't the colony, it's to develop and test the AIs off-Earth (where they've already caused to much trouble). There's also a team not in stasis, three people, one of whome has the job of killing an AI if (when) one of them goes crazy.
Perhaps this is Durandal's shame, that he was and was intended to be Bernhard's lab rat? That much is common theory; it is a theory the book suggests for the motivation behind the inclusion of the battelroids that I hope to offer. Perhaps Bernhard's purpose for the Battleroids was damage controll, if Durandal went rampant. What with the defense drones and his controll of the doors and what-not, Durandal could have caused a lot of trouble. It might have been feared that Battleroids would have been required to contain him in a worst-case scenario.
This seems to me to be the simplest theory that fits the evidence we have.
Again, if this has already been batted-about, I am unaware, and I am appologize.
