Is there a way, via FQL or the Facebook API, to access the wall posts to a fan page (not a profile)?
You can use Stream.get with the source id set to the page id of a fan page. I tried this on the developer console using the cocacola fan page (id 40796308305) and I think it accomplishes what you are trying to achieve.
This is the php example that the dev console gives me:
$facebook->api_client->stream_get('',40796308305,'0','0',30,'','','','');