I didn't expect Fremantle to be so open about this.
Only those involved could give the real reason for their approval, but I would suspect it falls along these lines: Documentary about a Price Is Right superfan gets the show good attention, maybe even the kind of attention that gets people to watch the show more and (more importantly) follow their social media stuff. Surely there will be those who are trying to "crack the code" so they can get on the show and break the bank, yet as we all know, the rotation and turnover of prizes has become much larger and shorter respetively since the perfect bid incident; thus, there's no real significant risk of the same kind of event happening again. I suppose somebody could really do their homework and happen to get really lucky if he gets on the show, but the odds of that are much lower than what they used to be. In the end, the show gets a bunch of good publicity that didn't cost them much, if anything.
I completely understand Roger being involved with this, but why Barker?
Why not Barker? Putting him in there only adds to the draw this thing can have. Plus, Barker gets to remind people he's still out there fighting for animals, but more to the point, I'm sure he would have some amusing anecdotes relevant to the subject to share.