The main reason I want to try this is that they are cheap, light and I think with the right servo and controller it will be very simple.......
In the first photo is the business end of the grabber, my thoughts are to cut the grabber short so it will be a viable fit on the ROV.
The second photo shows about where the hack should take place.
The third photo shows the mechanism for "grabbing" whatever. It seems very light to the touch and I have a feeling the mechanism inside the long arm is merely a sliver of aluminum that needs to be pulled and locked to maintain a firm grip. This would be only for smaller lightweight items, but I have a feeling it would be about what the weight limit is for the ROV in the first place...If we could mount the sliced grabber mechanism to the payload chassis and then find the appropriate servo that would work outside the ROV...we might have a nice hack!