Yes, blab is a Scrabble word!
...and is worth 8 points in Scrabble, and 11 points in Words with Friends
blab
Verb
1. Divulge confidential information or secrets
2. Speak (about unimportant matters) rapidly and incessantly
What Scrabble words can I make with the letters in blab?
3 Letter Words
2 Letter Words