I currently do a similar gig part time. No training needed--just have to get familiar with the ODG which is a pain at first then becomes really easy. Regardless of what the other folks say, I feel you can do these reviews and not be an insurance *****. It's pretty easy to see who is trying to do the right thing and who is abusing the system. For those trying to do the right thing, it usually turns out to be just an issue of documentation and them not being familiar with the ODG. I then call them for the peer to peer and coach them through it on how to get it approved. The outliers get denied and you get a little satisfaction to shut down a huckster that gives us a bad name.
Apart from some extra cash, you also learn quite a bit seeing how everyone else practices and you will have minimal problems with your own WC patients once you become familiar with the ODG (unless you're at the VA). You will also become more familiar with the literature which helps your personal practice. The ODG is not perfect but seems to be pretty in line with evidence based medicine overall. The ODG is after all just recommendations and if you feel it is not correct, you just support your recommendation with applicable medical literature. In addition to the ODG, there is a lot of WC peer review work out of California which uses the MTUS (based on the ODG guidelines).
I've been doing it about 2-3 years and made around $100K last year on peer review (most are TX WC cases, but some non WC stuff too). I spend 2-3 hours a day doing these (lunch break and a couple hours after the kids go to sleep) and most cases are straight forward. Number of PT sessions, whether an ESI is appropriate, etc. I see very few cases regarding causality and for those few cases use the "within a reasonable degree of medical certainty" line a lot (>51% chance). In other words, if it is in the ballpark it is workplace related.
You definitely take a tax hit with the 1099 income but the checks are nice until 4/15. With that being said, I am out of the peer review business as soon as I get out of debt 🙂