The Samsung GearVR unit had an adjustment that adjusted the effective focus, so the view would project the phone from infinite (and beyond) to near (at least 5 diopers). When I used mine, I was able to adjust it to do VR with no glasses, which was really nice, as other VR units did not have that and were awkward to wear glasses and VR. One pair of my PC glasses ended up with lens scratching from using another VR unit as a result.
So it depends on the device, but the Samsung GearVR at least has a focus adjustment that lets you set the effective focus distance to anything you want. You could even set it to the edge of blur to practice active focus with if that is your thing
The phone based VR setups (or any other VR unit) would be next to useless if they did not have a lens to push the effective focus point back. The phone is physically about 5cm from the eye, thus would require 20 diopters of myopia/accommodation to bring to focus naked.
Such a requirement might limit the market for such devices a bit