I suppose. And even for self-appointed busybodies. But, even though they say they are never off duty, the fact is, they are off duty for more hours in a week than they are on duty. One sees that in reports from time to time, "an off duty police officer ..."
Doesn't make any difference to analysis of this incident - Zimmerman is not a deputy. He's got the same rights and duties as any other citizen. My only point was that at that moment, he wasn't preoccupying himself with neighborhood surveillance.