The Oastlander rule:
"Self SUfficient: The men of Ostland have no desire to give their hard-earned gold to outsiders. As a result they can never hire any Mercenaries except for Ogres (who are not an uncommon sight in Ostland)."
The Triple Six Exploration result:
"You gain the services of any one Hired Sword (choose from those available to your warband) for the duration of the next battle, free of charge. After the battle he will depart, or you may continue to pay for his upkeep as normal." [emphasis added].
So, as the rules are written, Myntokk is correct - the ogre it is. But I would also agree with you and Myntokk both that given the rationale for the "Self Sufficient" rule, any hired sword that alignment/race-wise was not a conflict should be acceptable for the next game - you just can't keep the character by paying the upkeep after the first game, unless it was an ogre bodyguard.