Tho I half expected that Sam would be able to see Al, given his whole psychic thing. I don't know much about QL, but from what I've read, (mostly in author's notes to other fanfic crossovers!) there WERE a few times in the show when someone else could see Al. It usually had to do with altered brain chemistry - verge of unconciousness, brain damage, "touched" or mentally deficient individuals, etc.