Can the POTUS be charged with Dereliction of Duty as CinC? What would constitute this and what might the ramifications be?

No, He cannot be so charged.

At no time will he be subject to the UCMJ, not being a member of the Armed Services. The POTUS is not AT the top of the military chain of command. He is ABOVE the top of the military chain of command. While he can command the military (CinC), he is NOT part of it.

While a sitting President, he can be impeached and convicted (two separate things, from two different houses of congress) of high crimes and misdemeanors. He can also be sued as an individual. It MIGHT be possible to bring criminal charges against him while sitting, though I believe any action on them would be deferred until his term(s) was complete.

No he is a civilian and is not held to the UCMJ however, he is held to the United States Code, the United States Constitution.

Congress can "sue" him to do specific things, however he does have what is referred to as "Enforcement Discretion" & "Prosecution Discretion" as head of the Executive Branch.

In other words, he doesn't have to do "everything" exactly as written. He has the ability to "interpret" laws, and dedicate resources in the best ways.

For example, Congress passed the Controlled Substances Act:

http://en.wikipedia.org/wiki/Controlled_Substances_Act

He is currently not enforcing parts of it (Recreational Marijuana in CO & WA). Enforcement Discretion.

We have also seen "Prosecution Discretion" which is something as simple as letting someone off with a verbal warning rather than a speeding ticket. Sometimes it costs more to conduct a trial than the crime is worth.

So that said, the President can argue that he is well within his powers NOT TO DO SOMETHING. That it actually makes sense to ignore a specific duty for the "greater good" because he is focusing resources to something more important.