Welcome to the forums, Bkwyrm. I'm so sorry about the experiences you and your dds are having! Argh!
I have a dd who has life-threatening food allergies, and yes, I've had to quote the ADA
Multiple times. Our brick walls actually happened in public school, not in a special program, and some of the teachers/administrators we ran into were, quite simply, clueless. Clueless about the law, clueless in understanding life with a disability, and sometimes just generally clueless about humanity. For instance, an administrator at my dd's public school once told me (and I quote): "Yes, we could provide her a 504 after she's had an anaphylactic attack at school and she died." (as a follow-up to why they couldn't provide a 504 plan to her while she was still a living breathing student). So yes, I'm not surprised you're running into this type of issue.
A few things to consider: 1) Who is running the specific programs you're trying to send your dds too? The power of bringing in the ADA quotes comes when you are dealing with an institution that receives Federal funding - if they are receiving Federal funding then yes, they *have* to comply with the ADA. I think (and I'm not a lawyer or even well-versed on this, so I could be entirely wrong), that if it's a private business that's not receiving Federal funding, there is more freedom for the business in saying yay or nay to who attends and participates in academic programs. The size of a business can also make a difference. So.. be sure you're absolutely certain that the program must conform to the ADA and can't deny your dds attend.
2) Consider that the people who put up these brick walls are also the people who are planning and running the program you're trying to get your dds into. I spent a lot of time and effort advocating for my dd at her first school during K and 1st grade, only to be shocked to the core when I found out through an accidental remark of a parent how a certain teacher *really* felt about food allergies (as in, didn't believe they were real and thought it was just a pushy parent thing). I also saw over time, that even though we had a plan that the school agreed on that should have kept my dd safe, if the staff didn't buy into feeling that it was necessary, it wasn't much of a plan. So - be aware that you can advocate like crazy, get your dds in, and then possibly be among people who either don't want them there or don't take their need for insulin seriously.
I'd also really question a camp that said you (parent) can't come in - why would they say that? Regardless of the reason?
Last suggestion - if you continue to run into this issue with gifted camps, consider trying science or art or camps that your dds are just generally interested in. We don't have gifted camps in our city, but my kids soaked up the other camp experiences, and there were often other gifted kids enrolled.
Best wishes,
polarbear