Good advice going on here!!
Good question!!
Correct answer: You want that QT tank (which is
not also a hospital tank, ideally) to be as much like a display as possible. If needed they should be able to live there in the short term without issue.
Typical QT's you see around online are what I refer to as prison-style – too small and too spartan. Who'd want to live in a tank like that??
On the other hand, even a nice QT
does not have to be fancy – remember it's temporary.
So I DO recommend a nice piece of live rock and some plastic plants as a minimum.
If you happen to have to medicate then either consider the rock a loss and use it in your garden, or just brace yourself and add it to your tank anyway. Remember, seawater is not pure (
at all) to begin with and dillution is
heavily in your favor even if medication really can stick to the rock or whatever we're in fear of. I might qualify that depending on the med you ended up using, but that goes for anything conventional. A clean seawater rinse is all I'd do...perhaps a period of time in the sump, out of light while the display that "grows over" the QT tank rock.
BTW, need to medicate should be
unlikely since you're not crap-shooting your fish – follow your instincts; do it right; cross those bridges when you come to them.

Definitely don't worry too much.
The rest of this is just FYI....
You obviously don't have to go by my experience, but I worked 5+ years at a popular salt store and only had to medicate a tiny handful of fish. That was out of many many thousands. 364 days out of the year my hospital tanks were dry.
Most fish got a freshwater dip on the way into the system and then
TLC. That's it.
For what it's worth, the worst common occurrence for us was flatworms (cured with additional freshwater dips). A distant second was ich, which was generally treated with freshwater dips and even more TLC. There were only a handful of occasions where a whole retail system was treated with "ordinary" copper, with levels maintained daily via Hach digital colorimeter. (Store's closed, but the guys still do service....fish are handled the same.)