My little guy Titan appears to have a fair amount of wrinkles on the skin. Here are some pics from him. Recently upped his diet from 30 to 50 Dubias/day and he eats dandelion once a day (about 15 pinky nail sized pieces) that have been soaked in water. I also mist him a few times a day on his head. Gonna add some pictures in a second.
The wrinkles are normal and not really a good indicator of hydration. They can expand and contract their bodies quite a bit so it's helpful for their skin to be loose and flexible to allow this.
They can usually get enough hydration through their food if they are eating live bugs and fresh veges. A good indicator of hydration is their poop. If that doesn't look dry (or if it is accompanied by a puddle) then that's a sign that they are getting enough hydration.