My default search actually does display comments as I have a plugin called search everything.
I believe there is an option in Ajax to override or not the default search, right?
So if I don't override it – comments do come up. If I do, then I think the category selection for the posts is lost.
When you say categories – I'm assuming you mean excluding comments coming up from categories that have been excluded? That would be wonderful & very critical for me. The excluded categories are private and hold intellectual property – so comments cant be visible.