mma2

I own a X-H1 and sometimes use it with a couple of vintage 1950s Leica M-mount and LTM mount lenses via adapters.  IBIS works very well with these lenses and will also do so with adapted Nikkors.
Regarding IBIS, Fuji claims maximum IS performance when Fuji OIS lenses are mounted on the X-H1 and both the OIS lenses and the X-H1 have been updated with the latest firmware for each, respectively.  Adapted lenses will have reduced IBIS performance.  My experience with my adapted lenses has reflected this. IBIS allows me to hand-hold my adapted lenses down to a shutter speed a stop or two higher than a similar focal length Fuji OIS lens, but 3(+) stops better than what I can achieve with IBIS turned off or when the same lenses are mounted on my X-E3.  I am thrilled with this aspect of my X-H1's performance.
Hope that this helps.