I haven’t seen any Rambo movies yet either. I don’t think that mattered much in my enjoyment of this.
I was extremely surprised to see Ryan Stiles. I didn’t recognize him in the first one, so that counted as an extra surprise, after the fact.
I saw Andreas Katsulas’ name in the credits and said, “WHAT?” then found out which character he was and re-watched his scene; once I knew it was him, I was immediately able to hear his voice in…his voice.