I found this quote from Brian Smith, from December 26, 2014:"SteadyShot works either with half press of shutter OR in any magnification mode."
Sony A7II SteadyShot: Switching from OSS to Manual Lenses
So this apparently also implies that any non-native lens can benefit from Sony's version of IBIS, that they call OSS, not to be confused with their traditional lens OSS.
That was great news for me, so I tried it out with several of my adapted Leica lenses and the Mitakon ZHONGYI SPEEDMASTER 50/0.95 which has an E-Mount.
Indeed, that seems to be the case!
I focused a 50, 90, and 200 mm lens in magnification with the A7RII's OSS either set to ON or OFF.
Of course the fitting focal lengths have to be selected when changing them.
Then I exposed images at 1/15 s handheld.
The difference when focusing in magnification with OSS ON and OFF are quite striking to see in the EVF. As are the resulting images.
For me that means more precise focusing and shooting at lower shutter speeds when handheld.
As a result, my Mitakon lens will see more use handheld at f/0.95 on the A7RII than it did on the A7R.
As a side note, I have now paired my A7R with the Sony FE 2.8/90 MACRO G OSS lens, in this case the lens providing image stabilization.