Do any of the g-things work natively in Poser?

NO.

(by 'natively' I mean does it install from one or more executables cleanly, with no muss, no fuss, and no loss of advertised functionality).

You can kludge it in. You can even run the three or four extra python scripts floating around out there that provide some of the missing functionality sorta kinda if you're lucky. Assuming your system can handle the extra load if the scene is large. But no matter how you attempt to phrase it, a kludge is still a kludge, and loss of functionality is loss of functionality.

'Genesis' is nothing but a resource.

A resource that requires multiple steps and programs to achieve the function of a similar resource that is more than a decade old (never mind the functionality it claims) is not worth the time it takes in any environment where there is time pressure. Sure there are lots of tinkerers in Poser-dom; but if you notice, tinkerers do it for the love of the challenge.