Just wondering...

I quite doubt that. Most of them are Windows games running under Wine, DOS games running under DOSBox/Boxer, or running under ScummVM.

I'm uncertain, but I don't think Wine is retina-aware, so those games will effectively run at half-resolution (or scaled up to that from whatever the game supports).
DOS games don't support that high resolutions, and will run scaled up (whether to retina-resolution or half, I don't know - depending on whether Boxer is retina-aware).
ScummVM games are 2D and run at fixed resolutions, and as such will also run scaled-up (ditto, I dont know whether ScummVM is retina-aware).

I cannot answer for the rare few games that are OS X native.

Right. Like all these older games even offer support for those ridiculous resolutions. In fact, most GOGs don't come with higher resolution than 1024x768 (or below).