The contribution comes from their house edge.  Look at the dice game, base return is 99.0, then they take 50% of their profit and stick it in a progressive pot.  That's no different than any of the 99% dice games for the average player, there's just an additional and optional aspect of the game that some might find fun.  To be clear, the odds on these games are common odds found at many online casinos, the casino itself is donating a portion of its profit to the progressive pots.  If people don't like the progressives, they can completely ignore them and be happy knowing that they're receiving the return stated in the Base Game row of BVC's expected return page.

As far as the bot complaints go, they're ridiculous.  If people think a bot will help them they should be building their own or looking to purchase one.  I did build a bot, it was able to do something like 10 requests/second before running in to database sync issues on the site's side.  Note that's 10 requests/sec, not games/sec.  In video poker, that's 5 games/sec.  BVC's fast setting plays a game about once every 2 seconds, so it would have been quicker to open 10 tabs and hit the auto button than building a bot.  The fast setting on slots plays about 2 games/sec, 5 open tabs would be the equivalent of my bot.  The only conceivable advantage a bot may have over others is the ability to monitor the progressive pots continuously and automatically start and stop betting, but this does not give anyone any kind of advantage in actual game play.  It is wholly possible to achieve the same games/sec as a bot with multiple browser tabs and the in game auto function.

All that said, it is completely possible that BVC is playing their own progressives, and I think that might be an issue for some people.  They say they aren't, and the burden of proof lies on the ones making the claim in the affirmative, so at this point we have to assume that they aren't until such time that someone proves they are.  Additionally we know advantage players exist, so Occam's razor applies.