I think are many in high(er) stressful or risky jobs that do not turn to substance abuse, but in Nilan's heyday alcohol, cigarettes, cocaine, etc...all were pretty much acceptable.
Does seem goons have more serious mental issues than other players, not sure of stats on that (Is it any different in boxing, or UFC?)?
But, i think things are improving (fewer goons, much more support, substance abuse not as accepted, less stigma for seeking help), is great that Nilan did that for your father, overcame his demons and he does seems to be relatively happy camper these days.