Maybe I missed it, but I’m not sure I saw where anyone stated that the manufacturers were in bed with LP. What is more likely is that some may have turned a blind eye as the volumes that LP was moving should have been hard to go unnoticed. I don’t find that too hard to believe. The manufacturer is making money on those sales, a distributor is most likely in the middle, so the OEM has plausible deniability.
Without a doubt, LP used to deal in gray market items. As I mentioned, they were up front about it. If the manufacturers warranty wouldn’t apply, they offered their own. I’ve purchased a few items from LP, I’ve also used LP prices to purchase from LDSes that had a price matching policy. Some figured out ways to try to compete, some complained.
All of that is in the past, though. Pretty sure that LP/Scuba.com is now authorized for everything they sell, which means that MSRP or MAP rules with the manufacturer apply, so any discounts should also be available from your LDS.