I don't believe anyone can be an addict without actually having a psychological or physical dependancy to the drug. It's, however, irrefutable some are biologically predisposed to addiction.
People will say things like, "I was born an addict". Not so. How can I be addicted to meth if I had never tried it? Some are more prone to addictions, others are more drug or habit specific.
When I was in NA, I was always told I was addicted to everything - that addiction is addiction. I rejected this idea, as it is certainly not true in my personal case. I smoked weed [heavily] for years, but stopped because I was bored of it. I haven't smoked pot, nor do I think about it, in 4 years or so. I drank quite a bit for a while, but stopped because it was just kind of whatever to me. I might have a few beers here and there, but I rarely think about it. I used heroin heavily for a while, but stopped because that drug sucks. After the withdrawals, I didn't experience any psychological attachment to the drug.
Meth, on the other hand...
With that said, I think abusing any mind altering substance while fighting drug addiction is stepping on shaky territory
I remember reading somewhere at some point (maybe it was in rehab) that the brain actually changes once addicted. I'm not familiar enough with pathology to assume this implies addiction is a disease.