The fact that he's been highly successful, much more so in his playing career, does not constitute evidence that he's a workaholic manager and even if he's not that does not mean he won't succeed with us as I stated.
His current behaviour, in conjunction with some things I've read about his time at Southampton however, suggests that he's not type to dedicate a lot of his time to all aspects of the job.
You don't need to be a workaholic to be successful in a job. Koeman is the boss and if he trusts his staff then he doesn't have to be a workaholic. Workaholics are usually meddling people who think they know better than everyone else and the world will cave in without them.....in other words they have a lack of trust in other people and try to take on too much resulting in being ineffective.