This situation is out of character from the Aldora I know. They bend over backwards for you. I'm diving with them in May. But I should add, I am a competent diver, show up with working gear, don't create drama. If I showed up with broken gear and not dove in over a decade, I would expect a slightly different experience. If you show up as a GUE diver and wanting special treatment, well, that's just not going to end like you think on any number of operations on Cozumel.
Lastly, I was told the DM checks the O2 level as they load the boat and setup your gear. Remember this is a boutique operation that takes care of your gear. I understand the desire to check the O2 levels yourself because that is your training, but as long as they are checked I am fine.