I'm not certain, but I don't remember Jukaga being anything more than a politician. He may have been close to the Emperor, but I don't think he was a member of the royal family; thus I would suspect ineligible. We do know from the games that Thrakhath got the heirship from birth as the firstborn grandson of the Emperor. We also know that the Emperor appeared to have the power to strip Thrakhath of his birthright and choose another heir from his other grandchildren; he eludes to this in a warning to the prince in one of the WC2 intro scenes, that should he fail he'd be replaced by one of his 'fifteen cousins'. This was before Khasra died of course. That said, it has been years since I've read Fleet Action, but I don't recall Jukaga being a relative of the emperor.