Well, Ive knocked myself unconscious before.
Usually after getting stuck in some weird spot running/jumping around town. I end up on top of some fence post and I can't get off and eventually my character takes like 178 damage and falls unconscious.
But no exp.
Even if you went into battle with Marnid and Borcha, made a note of their exp, then somehow got them to shoot you in the head, it would only be like when you hit a friendly troop for the kill/KO...
no exp.
Hmm that puzzle is intriguing, but I immediately think unsolvable. Perhaps in recruit from prisoners mod you might be able to do something like, save your game, fight a battle, making sure that party has one single type of enemy that is only one guy. Take the single enemy prisoner, recruit him, look at his stats. Then go back to the save point, and enter battle again, find that soldier on the battlefield and let him KO you. Come back to battle, KO that soldier, take him prisoner, recruit him, look at his stats. Compare the difference in Exp... which might be changing every level you are at.
I don't think exp really works the same for non-hero characters though, and that procedure I just imagined is ridiculously improbable.
Anyways, I think Dranton would maybe be worth more out of the Arena. I would bet that Sword Sisters and Hired Blades are worth more on the battlefield, too.