Most charters in Cali, FL, HI, Cozumel, etc are going to require AOW. They wont care about your GUE-F card or nitrox, but they will care about AOW.
It has been my experience, at least in Cali and Cozumel, that OW is all that is necessary for most charters. As a regular on Cali boats, I have been surprised at the lack of detailed inspection of certs. Most Cali boats are familiar with GUE and understand the increased rigor required to obtain one of their certs. Also, the charter masters that mention AOW (usually dive shops attempting to add value to their AOW cards) for specific sites also include "or advanced experience" to sign up.
What amazes me is that anyone thinks that AOW - with it's five guided adventure fun dives that often includes only ONE 'deep' dive - actually does anything to qualify a diver for almost twice the depth!
If a diver crossing over to DIR through gue fundies or UTD Essentials finds themselves in need of an AOW card, they could get AOW equivalent by taking gue or UTD Rec 2.
cheers