I think soldering could cause the cable to fail where the solder ceases and the cable goes on without. This is a hard spot in the cable and will end up being a focus point for flexing and vibration, eventually leading to metal fatigue. I know the American Boat and Yacht Counsel (ABYC) does not recommend soldering when crimping amp type fittings to electrical wire in boats. This is a similar application, exposed to high vibration and movement.

My personal opinion is I will not solder this type of fitting due to the above.