Sure. People often want to conduct an IAmA in a small specialized subreddit where they can interact with their fans. That's no problem. You're free to raise awareness of it by posting in /r/IAmA, but you have to do it in a specific way so that people know that the questions will be answered elsewhere. Your headline should indicate who the person is and where the AMA will be taking place.
All crossposts must contain [Crosspost] or [xpost] in the title. Crossposts will be automatically locked by AutoMod to ensure questions are asked in the correct AMA thread.
Furthermore, cross-posts of AMAs that would not be allowed in /r/IAmA in the first place are not allowed, so make sure the AMA meets our standards of acceptable topics.