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I see no reason why not. As long as your character himself is not downright evil there's nothing in the rules to go against it. Besides, with the entire Cheliax faction dedicated to Asmodeus it'd be dumb to say the least not to allow Clerics from that faction to worship Asmodeus. They'd be forced to take a LN alignment though and couldn't pick up the Evil domain.
I take offense to that. Not every Cheliaxian is dedicated to Asmodues.