The only "Planet Bluegrass" campsite that does not require a 4 day pass is Lawson Hill.
From what I know from other posts you can camp there if you have a single day pass, but I don't know if you can camp there for all four days if you only have a single day festival ticket.
There are plenty of campgrounds around the area that are not under the control of Planet Bluegrass that people can camp at and still get into town for nightgrass or single day festival.
We need a confirmation from the staff on the rest of your questions.