Could Rear end damage from a wreck cause my speedometer and gas gauges to stop working?

You must understand that collision stresses the ENTIRE vehicle. Just because it was hit from behind, does not mean that there is not collision damage in the front. I had a vehicle in my shop several years ago that was hit from the rear. The engine began knocking shortly after. It turned out that the collision had jarred the engine hard enough to cause the crankshaft to crack. This type of damage is extremely rare, but can happen. Trying to convince the insurance company that this was collision damage was a real trick.... On the other hand, fuel sending unit failures are quite common (without any collision) and can cause your fuel gauge to stop working.

The only way to determine if your problems are caused by the collision would be to first diagnose the problem. Only then can it be determined if the current failure is caused by collision or possibly caused by a more commonly known failure type.