If you're thinking you'll be able to just dunk assembled or mostly assembled racks in at a time and clean them, it just doesn't work that way.
Also in a cleaner that big, if you want to use a 50/50 mix of simple green for example, you're looking at $10-15 in just cleaning solution each rack unless you plan on using dirty water repeatedly. If you want to use something like detergent, well then you will have very immediate corrosion problems.
For example if you used dawn and leave it in overnight it will look something like a coral reef later. So all those places that are hard to dry out when when they are still assembled are going to be susceptible to that corrosion.
Ultrasonic cleaners have a lot of quirks to them and they can actually cause damage in some cases, so you have to know what you're doing and be careful.