The action of shifting from forward to reverse with the wheels stopped will no more shock the driveline than reversing normally from a dead stop.
The larger issue here is spinning tires, as fishy pointed out. A few things to keep in mind:
Diffs are stronger in one direction than the other. Depending on your pinion orientation, you may have a stronger diff moving forward, or a stronger diff moving backwards. When you drive on the coast side of the gear, the diff has less resistance to grenading.
Second, with unlocked diffs, you are likely spinning one wheel. Not only is that wheel spinning twice as fast as the ring gear, it is getting 100% of the torque supplied by your front output shaft of your transfercase (assuming center diff locked, or traditional transfercase) where in normal operation, it sees 50%. That is more of a concern for axles, than diffs, but it is a common problem for open diff trucks.
Either way, I think the message is: avoid spinning tires if you can. It is necessary sometimes, but if you can avoid doing it, so much the better. Parts have memory. The more you stress something the more likely it is to fail the next time. By minimizing situations where you are torque loading one side of the diff or the other, the more likely things will hold up when you absolutely have to.
And, body work is usually more expensive than driveline work. Not always, but you can make junkyard driveline parts work more easily than junkyard body parts, unless multi-colored trucks appeal to you