A very good question and a considerably complex one. An individual with Narcissistic Personality Disorder is pathologically co-dependent on others, that much is true; however, they are co-dependent in a different context then an individual who has clinical co-dependency. The main difference being in the fact that an individual with clinical Narcissistic Personality Disorder has no sense of self outside of how others view them.
Let me explain, both individuals rely on others for their sense of self-worth, esteem and social function. However, should a clinical co-dependent be isolated, with no others to interact with, they would retain a sense of self. Though meager and certainly fragile, they have their own sense of identity. A pathological narcissist, on the other hand, does not and would turn to either suicidal ideation or would fabricate an illusory audience to provide them with ‘outside’ feedback.
Both are of the opinion that any attention is good attention; though some forms of it are more desired, any is more than nothing. A co-dependent fears the possibility of loneliness and the concept of being alone. The pathological narcissist fears not having narcissistic supply, to have their life remarked on, and the only way to gain supply is through outside sources.