As someone who has played Scrabble for decades, once my mother-the-English-professor discovered the game, I definitely have opinions. Mom, who is a stickler for rules, is the person who taught me that QAT is a word (and checking just now I find that the Apple dictionary allows it as a variant of khat) (plus I just learned a new word that starts with K). She liked to use the Scrabble Dictionary as her dictionary of choice during games, but I didn't agree with some of the collections of letters it considered actual words. These days, with the various online games, each of which has chosen its own electronic word library to use, some games leave out nouns that have been commonly in use my entire life, while accepting some things as "words" that I can't find in any dictionary.

My mother objects to using the OED as the game dictionary, because it contains so many archaic (and Scottish) words that are no longer in use. She and I do agree (as do the Scrabble rules) that proper nouns are not acceptable. Recently Scrabble came out with an edition for the younger set that allowed proper names, including personal names (like, say, CHAZ), but we will not talk of such things. I think what the best thing to do is to decide on these ground rules in advance (Mom and I never made someone miss a turn for playing something not in the game dictionary, for example), then have fun.