I'll give it a go in another 8-10 years. It's gained some traction over the years as an extracurricular activity among older white collar businessmen.
Here in the UK, it's something done by guys from all walks of life which seems to me to be something different to how it is in the US. Whitecollar boxing/Unlicensed/"Semi pro" etc has all merged into one with guys like Nick Blackwell coming up through unlicensed boxing rather than the amateur system, though that's something very different to what the OP is talking about. It's very popular here and it'll be interesting to see what happens when the first boxer dies during an unlicensed event.
The kind specifically mentioned by OP, free training and then a bout by guys who've never boxed before is something you get a lot of with charity Police vs Fireman type events. Normally 1-3 rounds, sometimes even just a minute a round. Usually headguards and 16oz gloves. Often the officials will just be the promoter's pals or whoever from one of the gyms, depending on how big-time the event is. And sometimes every fight is judged to be a draw with no winners or losers.
I don't think it's a good thing to do if you are serious about boxing. You need to be able to defend yourself properly to go into any competitive arena in my opinion, and a lot of those types of events are run like shit. Not all, but a lot of them. But then again, maybe just a one-time thing for the experience will be fun for you. It really depends who's promoting it and putting up the event, if it's a reputable gym and group or if it's not. Personally I'd think it would be a bad idea for you if you have back problems to go into a bout with only 8 weeks training. Just my opinion. Your body definitely won't be able to properly handle being hit, you'll be very tense on the night, and it might aggravate any existing back problems you've got going on. The truth is you will learn hardly anything in 8 weeks time that will be applicable on the night and you and everyone else will look crap and perform crap and that to me seems dangerous.
For reference, I've helped coach, corner, and I even judged at an unlicensed event in the UK before (which was a weird experience). I've been to one whitecollar event in the UK which was actually really impressive in terms of how it was managed and was put up by Amir Khan's gym for charity, and then I've been to many others which were just dire and shoddy.