According to https://clang.llvm.org/extra/clang-tidy/checks/list.html, modernize-use-override is the actual check while the others are aliases. But modernize-use-override is missing in Visual Assist. It must have slipped through. Please add it.
I think what is happening is that you have turned On "Show Unevaluated Checkers" in the Code Inspection settings. It turns out while this shows the unevaluated checkers, it ONLY shows them, so it is hiding "modernize-use-override" even though this one is also in the list, its just an evaluated checker.
I ended up thinking the same thing, it would make more sense to add the unevaluated checkers to the list, rather than only showing the unevaluated ones. I have put in a feature request for this: