"Are Viton hoses just a name, are they chlorinated polyethelyne?"
I think you are referring to something other than Viton. They are a different material altogether.
http://www.dupontelastomers.com/Products/Viton/techInfo.asp
says: "Viton® consists of essentially several standard and specialty types of polymers based on their composition and flourine content.
The types differ primarily in the end-use performance of parts made from Viton®. Each type differs in its ability to: resist permeation and volume increase, resist attack and property degradation caused by the chemicals and fluids."
I am using Viton return hoses on the injectors and its holding up really well, in another year I'll have about 16 months service at which time regular OE return hoses will have started weeping (or worse) so I'll report more at that time.
I am not suggesting Viton return lines for cars with the 617 engine as they need regular valve adjusts at which time the return lines are typically replaced. In cars with a 603, 606 etc. engine with hydraulic valves Viton starts to be attractive for return lines.
In cases where 100% Bio fuel is used it is said that Viton will not get soft and leaky like the OE rubber hoses. I have not seen that because I haven't had that experience (yet!)