Actually, the only person that Obi-Wan connects with the word betrayal is Luke's father, and that was all a lie anyway.
He says that Darth Vader "helped the Empire hunt down and destroy the Jedi Knights."
And that could mean just about anything. Though as I discuss in a sepeate topic, there could be considerably more than 10,000 to go through...
I can't remember if the Reek dies. I have to go and check. The Reek's just a crucial element in the fight between Jango and Mace. It stands between them but it's very dangerous to get close to him. Mace looses his sabre during the fight, the Reeks steps on it so he can't Force-reach for it, stuff like that.