^ It definitely can be, especially the part where you provide benefit and value before monetizing in any way just to attract a semi decent sized userbase, then actually monetizing it without pissing everyone off for making dough from their collective input and content... Having said that though, there's a lot of value in just networking, so owning a community (especially marketing/business related) does have its perks above and beyond making money from them or their clicks/eyeballs.
EDIT: Just monetizing a forum as an aff/vendor, only real way is to go direct and strike a deal w/the owners for media space, sponsored threads, cross promo discounts brand to brand etc. Black hat is another ball game I'm sure but yeah trying to just stick aff links on forums is rather pointless.
I will say that with my forum i don't bank from the members, but we all bank nice launch after launch as a team. Of course only the strong survive like with anything but the value in this specific scenario is having a huge base to pitch offers to as a vendor or group of vendors.
One last point: Tried to run a continuity forex program back in the day, it came with private access to a top traders forum that we started. It started off great, but back then the competitors in the fx niche were (are) fucking dirty, and our forum got attacked non-stop for a month or so straight with everything from injections, spam, illegal porn, 1000's of members seeded, no matter how tight we made the fucking ship we just got swampled by outsourced Russians and eventually traced the shit back to one of our rivals... closed the forum down altogether (This shit was part of a $250/month offer too). They just wanted us down, and had the resources to keep it up long enough to force us to close it/got sick of defense.