Rugby should actually provide a decent athletic base for combat sports, obviously he needs to have his striking and grappling skills to get to a high level, but Rugby training should give this guy excellent cardio and perhaps some mental toughness.
I think most people outside of the rugby world tend to underestimate the CARDIO needed for Rugby. 40 min halves with very minimal stoppages, similar to soccer, but in addition to all the running (the whole team runs the full field) there is the tackling, pushing, shoving, scrums etc. it is pretty grueling activity. No 40 second rest between plays like American football.
Hopefully this guy can fight, the HW division needs new talent badly.