We do know that rakebacks do exist but not into that insurance thing.Who would be the hell would be giving out such service if they do know that gambling does involved on being on the losing side most of the time?
Therefore, no gambling site that has incentives, that's impossible. Just accept your losses if there is.
It's a promotion in the site, I do read that kind of promotion "rakebacks" from some of the sites but if ever there's an insurance in gambling, it should not be the gambling site who will provide and insurance but the 3rd party which you are right does not exist.