Okay, this guy is nuts.
No, really. The Pirate is a big guy, but he's understaffed in the mental department:
There was a shrinking in the Pirate's eyes when he confronted any grown person, the secret look of an animal that would like to run away if it dared turn its back long enough. Because of this expression, the paisanos of Monterey knew that his head had not grown up with the rest of his body. (7.1)
So, fine. The Pirate's not the sharpest pencil in the box. What else can we find out about him?
Well, get this: the Pirate's dim-wittedness keeps him innocent. Whereas Pilon and the rest of the gang are con artists, always looking for their next victim, the Pirate just goes about his business, making an honest day's living. This, of course, leaves him vulnerable to the others' scheming, but it turns out that he's such a chill, innocent guy that even Danny's friends can't bear to steal from him. In fact, they end up being his allies.
When the Pirate tells the friends that the money he's hoarding is totally for a candlestick for Saint Francis, the friends know that the jig is up: "So it was over, all hope of diverting the money [...] There was nothing in the world they could do about it. Their chance had come, and it had gone" (7.104). These rascals are super disappointed about the fact that the Pirate turns out to be such a good guy; he's so good that they can't even rob him. (So they do have some moral standards, after all.)
The Pirate's intentions are pure, and so are his thoughts. He never even catches on to the fact that the friends had originally tried to rob him. When they take his money back into Danny's bedroom to keep it safe, he feels nothing but joy:
The Pirate stood before them, and there were tears of happiness in his eyes, for he had proved his love for his friends.
"To think," he said, "all those years I lay in that chicken house, and I did not know any pleasure. But now," he added, "oh, now I am very happy." (12.105-06)
The Pirate isn't just happy that the friends are treating him well; he's overjoyed because he has proved his love for his friends. He thinks that he has cheered them up by coming to live with them, and that cheers him up. This dude is just a sweet, good soul, almost like a kid brother to the friends.
In a way, the Pirate's a symbol for what these guys have lost: they can't go back to being innocent kids again, as much as they might want to. And maybe that's a good thing: there's a lot to be said for experience, and it's hard to imagine what it must be like to go through life like the Pirate, always a little bit unaware of what's really going on around him. Ignorance is bliss? Maybe, but we're going to stay skeptical.