Can dysphagia lead dehydration?

Yes. If one has enough difficulty in swallowing, then one may not drink enough fluids to stay hydrated. This dehydration needs to be treated immediately and then the underlying disorder must also be found and treated.
Yes, only if........ If it is enough to decrease oral intake making input less than obligatory output ( sweat and urine). Usually the minimum losses are about 600-1000 ml i.e. 20-35 ounces. The warmer the weather, the more the loss is. If, for whatever reason, you intake is consistently less than losses, you will become dehydrated. This could decrease kidney function.