IMHO its fine to try to provide extra hydration for a chameleon who's eyes are sunken in but more often than not, the sunken eyes are accompanying an illness and thus just a symptom. IMHO you need to make sure that it is only dehydration and not something else.
Dehydration identification: are the urates white or not? If you take a pinch of skin and pull it away from the body, how fast does it return to where it was? Is the chameleon drinking?
"Signs that a chameleon might be sick include: sunken eyes (dehydration), not eating for days, listlessness or weakness, rapid weight loss, abnormal swellings, regurgitation, very watery feces, etc."....
http://www.exoticpetvet.com/breeds/chameleons.htm
http://www.ivis.org/proceedings/navc/2006/SAE/603.pdf?LA=1
Dehydration identification: are the urates white or not? If you take a pinch of skin and pull it away from the body, how fast does it return to where it was? Is the chameleon drinking?
"Signs that a chameleon might be sick include: sunken eyes (dehydration), not eating for days, listlessness or weakness, rapid weight loss, abnormal swellings, regurgitation, very watery feces, etc."....
http://www.exoticpetvet.com/breeds/chameleons.htm
http://www.ivis.org/proceedings/navc/2006/SAE/603.pdf?LA=1