As it was explained to me, it is possible the risk of OOB during bump firing is more related to the style of holding the weapon rather than the rapid cycling. The rifle can be jerked some funny ways if only supported by the hand guard instead of supporting hand, firing hand, and shoulder. This could cause some guns with floating firing pins (basically all military-style guns) to experience a heavy inertial strike (where the firing pin hits the primer lightly as a result of the bolt coming closed, the gun should not fire at this point but wait until the hammer falls). So technically if this occurred it would be a slam-fire that could potentially cause an OOB firing if the action hasn't closed completely. This type of problem would be exacerbated by certain types of ammo, poor condition of the weapon, and especially a dirty/fouled action that may have more resistance to locking into battery or gunk built up on the firing pin or chamber face that makes the inertial strike worse.
Disregarding the particularities of every gun (some models may have designs that make them prone to problems), in general, I suspect a clean weapon in good shape with decent ammo shouldn't have issues if held steadily.
YMMV, so do it at your own risk