Some of this occurs naturally. People who were deep enough into a niche to become moderators of a subreddit in the late 2000s and early 2010s are also likely to end up working in that industry or starting business in that industry.
However, many companies have realized that being in the good graces of subreddit moderators can be very good for their business. It's becoming common for brands to reach out to subreddit moderators with offers of free products or even paid job offers to bring them onto the company's side. I know of several companies that routinely send free gear to relevant subreddit moderators. The arrangement is "no strings attached" but it usually results in a favorable moderation outcomes for the company. Moderators have a lot of power to influence conversations on Reddit in non-obvious ways.
In some ways, having a subreddit that champions your products while maintaining an appearance of being impartial is better than explicitly spinning out of Reddit. People know not to trust positive Amazon reviews, but Reddit conversations are generally assumed to be authentic.