Specifically I'm curious if a hybrid executioner can choose a guild for the original (pre-Essentials) assassin, Bleak Disciple or Night Stalker. The assassin guilds do not come with any at-will powers, but they have some pretty nice features. These may be two entirely separate features with similar names, but I thought it was worth asking.
You can only choose from the Assassin (Executioner) guild choices (League of Whispers, Red Scales, or Way of the Ninja). The text of the Guild Technique ability from the Character Builder states:
You become a member of an assassin guild. You can choose to join the Red Scales, the League of Whispers or the Way of the Ninja.