Unless you are prepared to build some industrial strength equipment of your own design and then move everyone in the neighborhood away while you experiment with this, I fear you are taking your life in your hands.
Normal pressure cookers add a maximum 15 PSI to achieve a water boiling point of 121 C or 250 F. Autoclaves, used for surgical sterilization, go to 30 PSI. You are talking about going more than twice that.
There is no reason, based on the science of Maillard reaction, to believe that it would not occur at a high enough temperature. The presence of excess water would normally inhibit the process because of temperature reduction, but your "super duper pressure cooker" would keep the temperature at a high enough level to allow the chemical breakdown to occur. You might, in fact, discover that it occurs a bit earlier, as water tends to facilitate many reactions. Caramel making comes to mind as an indicator of what might be achieved, as sugar syrup (OK, most of the water is gone, but in principal) browns when you get in the above 330F-165C degree range.
As to crisping based on quick pressure reduction (perhaps when your device explodes?) That seems less likely as most crisping comes at the loss of water, and you are, in effect, keeping water in contact with your food both in liquid and superheated steam form. It would, most likely, be similar to a braised food surface, than a fried one.
Interesting thought. Please don't try this.
You can definitely cook donuts in a deep fryer. Most, if not all, donuts shops cook them in that manner. Just make sure your temperature is good and use something like chopsticks to flip them.
Best Answer
If you need a larger basket to fry the amount of food you want to cook, you need more oil as well. If you don't always want to make that much food (or use that much oil) then you need a smaller vessel for deep-frying, such as a second fryer or a small wok or kadai.
If you put less oil in than the minimum it may not cover the food and/or the oil could overheat, depending on how the fryer manages its temperature settings.
Overheating oil can be dangerous and will also burn your food while leaving it raw inside. All around, something to avoid.
You can save and reuse frying oil. There are some good tips at the sites below.
Let it cool fully then filter out food particles (I use coffee filters and a funnel for this; it can be a slow drain, be patient)
Refrigerate used oil to retard bacterial growth
Stop using it if it looks weird or smells funny!
http://www.seriouseats.com/2013/09/ask-the-food-lab-how-many-times-can-i-reuse-fry-oil.html
http://extension.psu.edu/food/preservation/faq/questions-and-answers-about-re-using-frying-oil
http://www.epicurious.com/expert-advice/you-can-reuse-frying-oil-article