"It's Tracker. Yes, the Action Man thing is a nod, and if I recall correctly, Tracker himself notes that it's a "nickname", not a code-name or anything official. My copies of the book haven't arrived yet, and I don't have the script in front of me, but I'm pretty sure it's along those lines."
They are still two different people.
My No-Prize explanation....Action Man visited the Joes for a couple missions, the rest of the team noticed that Tracker and AM dressed similarly, and after Action Man left the team started calling Tracker Action Man as a joke.