I would have a major problem with a player who, on one hand, wants to play a Faithless character, denying the gods are worthy of worship, but on the other hand sidles up to the cleric every time he has a boo boo.
It's basically trying to eat your cake and have it too. "Hey the gods are a buncha bastards and nogoodniks. Now, make with the raise dead so I can keep playing this character." It's ludicrous.
If you want to deny the gods, fair enough. But that choice carries consequences. I'd pretty much write off that player as not really being interested in actually playing the character he claims to want to play.
It's a bit hypocritical, but people are very often hypocritical.
One of the main themes of my long-running campaign is that the gods are simply higher forms of being. They have great power and influence the world significantly, but they did not create the cosmos, nor the mortal races.
Some of the PCs in my campaign have become very aware of this, and they behave accordingly. We have a few different groups of PCs of various level. The highest level PCs are aware of the true nature of the Powers. They're also becoming increasingly powerful themselves, and are beginning to deal directly with beings of great power, such as Demon Princes and Lorda of Hell and Proxies of the Powers themselves.
They respect the Powers, but they generally no longer worship them. One of the PCs is a dwarven cleric of Moradin. He venerates Moradin as the patron of dwarves, but he is no longer under the illusion that Moradin created the dwarves. That doesn't mean that Moradin does not act on their behalf and is therefore worthy of honoring. So he honors Moradin and because he is a champion of the causes that Moradin supports, he receives spells, and uses those to help his allies.
As with so much of this debate, it's up to the individual DM/group to decide how all of this works. I personally can agree with a lot of the criticism of the whole Faerunian afterlife and the Wall of the Faithless in particular. If the gods are to be viewed as actual shapers of the cosmos and the creators of mortal life, then the Wall simply serves to show their imperfection, and therefore undermines their claim to authority.
I think it's an interesting concept and opens up tons of ideas and potential stories. But I can't really see such stories going any other way than to rebel against the idea of the Wall. Who would support such a clearly flawed system?