Dox about alcohol withdrawals:
Withdrawals from other drugs are usually not so dangerous. Heroin/opioid withdrawals might make a person feel like they are dying or want to die, but it doesn't carry anywhere near the risk of death as alcohol withdrawal.
With opioids like Oxycontin, heroin, or buprenorphine, there are a couple of other concerns besides withdrawals. First is something called "incomplete cross tolerance". That means that you need less of a substitute drug than your drug of choice to get high. So if someone is used to shooting 80mg of Oxycontin to get high and thet google the pharmaceutical equivalent of heroin and shoot that up, it's pretty easy to OD. The other concern is that the tolerance you built up to your drug of choice goes away after a period of sobriety. So if you used to shoot the 80mg of Oxycontin, get sober for a few months, and then go on an epic bender, the old reliable high of 80mg could now be deadly.
As an aside, I don't think it is strange or ill advised to hire recovering addicts. I actually know a few who have gone on to work for reputable treatment centers. The problem with Narconon is lack of training and supervision, imho. At minimum, they should be getting drug tested with some regularity.