OK back up the truck...the info that you have on ADHD and academic support is not at all accurate. ADHD is not a learning disability, it's a health impairment. In order to qualify for the academic support that comes with a learning specialist, a students needs to demonstrate a learning disability, which is determined by testing in the bottom 25% of at least one portion of a battery of tests that the school administers. There are many kids with ADHD who do not qualify for an IEP (which is what one needs to be on to be assigned to a learning specialist). If your son is not struggling academically, then there's a good chance he wouldn't have qualified to be "part of that crowd" (snobby much?). However, by not disclosing his health impairment, you have prevented him from being able to access support in the classroom via a 504 accommodation plan. If his academics are fine, then perhaps he wouldn't have benefited from them anyway but there may have been times over the years when he could have benefited from things like preferential seating, extra time on tests, or more support managing communication around homework, tests, and projects - those executive function and long-term planning tasks that kids struggle with. If his ADHD has manifested in any disruptive or irritating behaviors, it may have been helpful for his teachers to know that. The thing is, even if he did qualify for academic support, the IEP process requires parental approval and if you didn't want him to receive that level of support, you could have just declined that part of the plan and opted to keep whatever parts would have been of benefit to him. It's a shame that you did not have an accurate picture of how academic support services work so you could have made more informed decisions before.
So at this point, it really depends on whether or not he needs the academic support or any accommodations. Does he (and do you) feel that his symptoms are managed well enough with whatever treatment that's being used to manage this? Or does he needlessly struggle academically? How are his grades? How does he do on standardized tests?
If you feel that he could do better in school with some support, then you can't just cough up an ADHD diagnosis and expect services. You have to go through the whole educational assessment process (request an assessment in writing, some testing gets done a few weeks later, then they meet to discuss the results). If it is determined that he does qualify for support services, then you can figure out what your options are for next year.
My oldest son has ADHD and learning disabilities and has been on an IEP since 4th grade (he's in 9th now). He has one period a day of academic support and would drown without it. It's not some kind of frivolous perk and really isn't supposed to be used for homework. He spends as much time on homework at home as his step-sister who is in the same grade and doesn't get support. He uses the AS period to study extra for tests, work on projects, or re-do homework that he didn't understand or do thoroughly. The down side is that he does lose out on the chance to take an elective class and really wants to. His goal this year is to demonstrate enough proficiency to be able to drop down to AS three days per cycle next year. He'll be able to drop to 3 days of PE and then take an elective. So we'll see how it goes - he would much rather be taking another interesting class than spending a period in AS each day, but right now he really needs that time each day to stay on top of things.
One of the benefits of being on an IEP is that in addition to academic support, he get accommodations for standardized testing, including extra time on the SAT. I have tutored many students over the past few years would legitimately could have benefited from extended time on the SAT but didn't qualify for it because they weren't receiving services in school all along.
At the end of the day, it come down to whether or not he needs academic support and if so, how much. To me, school is a partnership between parents, students and teachers - I can't imagine leaving the school in the dark about something as important as a health impairment that could negatively affect my child's performance and behavior. He'll never be forced into accommodations or services that he doesn't want, and will not have access to things unless he qualifies for them anyway.