Yes, folk is a Scrabble word!
...and is worth 11 points in Scrabble, and 12 points in Words with Friends
folk
Noun
1. People in general (often used in the plural)
2. A social division of (usually preliterate) people
3. People descended from a common ancestor
4. The traditional and typically anonymous music that is an expression of the life of people in a community
What Scrabble words can I make with the letters in folk?
2 Letter Words