I think you need to consider your definitions very carefully.
"Gaining mass" can be applied to those looking to gain weight in whatever form while bodybuilders really are only looking to gain muscle at the end of the day.
"Definition" is promised by tabloid/infomercial diet and exercise plans. It is not about gaining muscle but about losing fat.
My point is neither of these terms are defined by nor define bodybuilding. The terms have larger cultural meanings.
I am not trying to be persnickety but I think in the pool of those who do suffer/have "exercise addiction" few are going to be bodybuilders.
How you define bodybuilding is important as well. As with any endeavor, those who excel (in general) are going to be more focused on the activity than the general public - who may perceive the focus as obsessive.
Also, the length of time someone is involved in an activity matters. People who start lifting seriously tend to be more "obsessed" in the beginning because there is a lot to learn and work through. Those who have been doing it for years/decades have probably already found a way to balance their lifting/diet with the rest of their lives. Again, those outside the sport may find it excessive but I doubt that is always terribly objective. The focus on diet is probably similar or less than those who are vegan, suffer gastrointestinal problems, dieting, etc.
When you consider the amount of time people in general spend watching TV/movies, talking on phones, shopping, playing video games, etc. and then compare that to the time 'gym rats' spend in the gym, I would expect that in the vast majority of bodybuilders would be spending less time lifting that others spend on entertainment.
Those who I have seen (having worked and spent over a decade in the gym) who I would be tempted to say are exercise obsessive lived mainly in the cardio part of the gyms. The might lift but that did not seen to be their focus. This includes the people who would weigh themselves when they came in, when they left, and sometimes at different points in their workouts.
Short answer: I think "exercise addiction" is rare in the bodybuilding/weight-lifting community. I think it is more common in those who are trying to lose weight and or gain definition as their main goals.