Is Neddy trying to cover up his true weak, unlikeable, poor self with this heroic, athletic, wealthy image?
By the end of the story, the reader realizes that Neddy is not really trying to cover up the weak and poor image. Neddy has lost touch with this aspect of his life, whether through denial or a nervous breakdown. He genuinely thinks of himself as a heroic and strong person - which may be one of the reasons that led to his financial ruin, but most everyone around him (and the reader) realizes how pitiful he really is.
Neddy does appears heroic and strong as he heads out on his adventure to swim the river Lucinda. Yet, at each stop, we learn clues about Neddy's fate. He crosses an empty horse riding range belonging to the Welchers, yet he cannot remember what happened to them. Obviously, something has happened to his memory. This causes us to question Neddy's perspective on things? The Hollerans tell Neddy that they are sorry to hear about his troubles. Neddy appears to have no idea what they are talking about. The Biswangers, who used to be socially inferior to him, now treat him badly. His old mistress rejects him.
Ultimatley, he arrives at his house - vacant and locked - and the true nature of his despair is evident: he is evicted from his own life. This story is powerful in its examination of a man who believes his life to be one way, yet through the story itself, the reader is able to see that it is not that way at all. Worse yet, Neddy seems incapable of realizing that.
Yes and no. By that I mean, it is a bit more complicated than this. Neddy Merrill is having troubles in life, and is out of place. He chooses his actions in part to make up for these things, and maybe to cover up for them. That's true as far as it goes., and probably fits covering up his financial situation. However, he's also genuinely lively. He has a lot of energy, and likes to do physical things. In some ways, he's like a kid. You've probably seen kids run and jump for no reason, yes? Neddy does some things for reasons that are just as innocent and self-absorbed.