It depends. It depends. It depends.
As a bettor they shouldn't apply the RO to original balances for contests wins (unless otherwise indicated but preference is NOT) and RO otherwise should be bustable.
Hypothetically if I was running a book though, I would look to exclude sharp players/bonus whores and build a stable of losers.
So i would make RO on bonuses not bustable and apply to the original account balance + bonus + redeposits whether win or lose regardless (and offer slightly lower RO on bonuses because of it).
In addition would keep RO calc lesser of risk/to win capped at both ends.
Applies to contests, sign-up bonuses, re-deposits etc.
It would discourage bonus whores from running up high balances unexpectedly if they couldn't bust it out beforehand.
Of course advantage players who want to get down to hit off market lines, steam or their own advantage picks are different.
At least that way you can concentrate on weeding out their action from your books unless you wanted it. Fish take care of themselves.
Still all hypotheticals though.