I'm am sure that the max bets allowed in the games is probably set somewhere in the general bonus terms, and that some of the slots may not have very high bet amounts allowed. While not impossible, it's not that easy to take $10,000 up to $100K with 2 to 6 bets or whatever is allowed, especially with the exclusion of progressives.
I've not played Rival in a long time, but I still remember and still see screenies.
Even if it's quite EV poor, I would probably take this one. How many chances to we get to win $90K or so with $25 deposit? (that's assuming bonus is not cashable). If you enjoy playing the games it will be a heck of a ride with that kind of bankroll, and if you are very very lucky, no grinding once you get there.
If I were to take it, I would ask lots of questions, keep the emails and chat transcripts, play every game to my heart's content and hope for the best.