Since my last comment I have added a new work around that kind of works, but requires me to keep track of what is load shedded. I go to the generator and make it a 2 breaker generator. The ATS gets connected to breaker one. Breaker 2 gets a label called "Load Shed" and I manually put a -10 in the heater load if I am shedding a 10kW heater and -20 if there are 2 10kW heaters. DM then shows the correct load on the ATS/Service and a reduced demand on the generator.

Funny I was just thinking how most of my generator and generator panel load calcs are never accurate. That is because for most residential and many commercial generators there are load shedding devices that are connected by relays that will turn items off when on generator. The solution is to create an additional check box next to the load type called "Load Shed". Then on the one-line device set up you would include an "exclude load shed loads in the calculations" check box. I would say yes on the generator, ATS, and Generator panels. Problem solved!