Does having a gimball mean you can disbale stability on action camera
As Michael Clark pointed out when the question was on photography, it depends on the type of gimbal, how good the gimbal is and how skilled the operator is.  

An inertial gimbal works by giving the camera assembly a larger size and mass and then having the operator hold the assembly near the center of gravity.  When the operator moves, inertia slows changes in the orientation of the camera, resulting in smoothing of angular changes.  This requires the gimbal to be very near frictionless to minimize the impact of the operator's movement on the rotational inertia of the camera assembly.  A low quality or poorly maintained gimbal won't properly isolate the assembly and an unskilled operator may improperly balance the assembly or cause excessive motion do to the added weight and complexity of operation.

A robotic or motorized gimbal, such as a Ronan, acts on a slightly different principle.  They do not require the finesse of the operator to execute changes in camera direction as this is accomplished by a joystick (less direct control, but easier to operate).  Additionally, they are not quite as balance sensitive as the orientation correction is provided by gyroscopes and motors which can tell what's actually happening vs a simple passive physics based system.  Additionally, counterweights aren't needed for stabilization so the rig can potentially be lighter overall making it easier to handle.  The down side is the previously mentioned lack of direct control and the power requirements.  Additionally, the quality of the gimbal still becomes a major factor.  If gyroscopes are not sensitive enough or the motors are too imprecise or laggy, then the quality of the stabilization will be greatly reduced.

Both of these types of gimbals are designed for correcting 3 degrees of orientation and do not handle any lateral movement on their own (adding things like vest &amp; arm systems can add some position stabilization as well, but weren't specifically mentioned in your question.)

Image stabilization on the camera depends on the camera.  Some use movement of lens elements (optical image stabilization) to correct the direction the lens is pointed as the orientation changes.  Others use free floating sensors that are able to move in response to motion to keep the sensor in the correct orientation and location in the image circle.

The amount of correction that either of these in-camera systems can provide is extremely limited since they don't govern the actual aiming of the camera body, but they can help with a degree of hand shake.  There is one noteworthy distinction though.  For the floating sensor types of camera stabilization, it is possible to correct of a limited degree of positional stabilization, not just orientation as the sensor can move up and down and side to side a bit.

In general, I would expect that with a half way decent gimbal and even intermediate experience as an operator, you should get much better overall results with the gimbal, but depending on your shooting situation, you may still gain some additional benefit from the camera's built in stabilization if it has a floating sensor particularly.  You really need to try messing with it either way though as the movement may be sufficient to throw off the balance and cause issues with the gimbal as well.  

Certainly the effects should be pretty minimal, so if your primary concern is recovering the higher frame rate, then using a gimbal and turning off the in camera stabilization won't give you a major sacrifice in stabilization quality.