Yup dehydration and no desert snakes are never a good thing. Denting in eye caps are almost always hydration related. Thankfully they have very robust eyes that can take a beating so curing the hydration issue and husbandry can do wonders.

You must keep humidity at the required amount for the species you keep. If the snake has evolved in high humidity, they are more prone to issues if you can't keep humidity up.

Injecting prey is a good way to get hydration in fast but a snake will almost never refuse water in a bowl so long as it is fresh. If your snake stays dehydrated after taking steps to fix it (number one is keeping humidity correct), I would have the vet to a fecal test for parasites.