[winbig]

If you want to split hairs here (assuming $50D + $50B)

1: you're playing with your own money before any bonus money.
2: you can bet $50 on roulette and be safe (going by: Any use of bonus funds to wager on any variation of Blackjack Surrender, Blackjack Switch, Pontoon, Baccarat, Craps, Roulette, Sic Bo, Pai Gow Poker, Video Poker Double Up and Wild Viking is not permitted and will result in the loss of any bonus and winnings attributable to their bonus.)

But, if you REALLY wanted to split hairs, going to roulette and betting $50 of your own money just to increase your BR to go and play slots to complete the WR, I think most casinos would see that as bonus abuse.