engaged workaholic
n. A person who works compulsively because he or she loves their job.
Other Forms
Though unhappy clock-watchers (including some of Valenzuela's friends) may be tempted to call her a workaholic — endangering health, psyche and personal life by being too wedded to work — some researchers think there's nothing at all wrong with her. They think, instead, that she'd aptly be placed in a relatively new category that some call an "engaged workaholic." …

Engaged workaholics may dodge some or all of those nasty repercussions for one simple reason: They love what they do.
—Kathleen Doheny, “Workaholism: Maybe not such a bad thing,” Los Angeles Times, February 13, 2012
Engaged workaholics were driven by both controlled and autonomous motivation.

That is, engaged workaholics focus on the instrumental value of a job and meeting standards to gain self worth and approval as well as personally value their work. They were also found to spend most time on working.
—Katy Kamkar, “It is possible to be an 'engaged workaholic',” CTV MedNews Express, October 21, 2011
2011 (earliest)
A confirmatory factor analysis showed that workaholism and work engagement were two largely independent concepts. Crossing these two concepts yielded four types of workers: workaholic employees, engaged employees, engaged workaholics, and nonworkaholic/nonengaged employees.
—Ilona van Beek, “Workaholic and work engaged employees: Dead ringers or worlds apart?,” Journal of Occupational Health Psychology, October 01, 2011