I think that, to summarize - it’s OK, or sometimes even beneficial (rarely), to mention health problems in these cases:
A. They have been overcome, and are unlikely to be an issue in the future. However, they should not be mentioned in the context of “why my grades dropped”. That is something that the counselor can mention. In context of “why my participation in my favorite EC dropped” would be OK, so long as it’s not “why I did manage to win the so-and-so award”.
B. If it’s something that is a being fully managed and is manageable. For example, being hard of hearing or having mobility issues.
One must bear in mind that there are two issues from the college’s perspective: 1, they don’t really care what an applicant may have achieved, only what they have achieved, and 2, they are worried about liability and extra costs.
Oh, and finally, applicants should NOT use these health issues as part of a “How I Persevered and Overcame Obstacles” essay theme. That theme should be avoided entirely.