Exposed White or Clear Gesso

​Bare acrylic dispersion painting ground (gesso) does tend to yield a different sheen when varnished than oil paint, especially brands of gesso that are more “thirsty”.  Subsequent coats of varnish usually unify the surface finish, however. It seems to me that having passages of bare acrylic and oil paint on the same picture could introduce complications in terms of cleaning and care, but I’ll let the experts speak to that.

On a related topic, it’s important to understand that alkyd-based painting mediums generally don’t meet the standards of a picture varnish, in terms of reversability and in retaining neutral color as they age. A final varnish should facilitate removal with less aggressive solvents, something that’s really not possible in-studio with alkyd. Synthetic resin solution varnishes are really a good choice for almost all completely dry pictures that are ready to display. 

​Easy mistake, thanks for the correction. 

I do not believe that it would be disastrous to have areas of exposed acrylic dispersion ground showing but the exposed ground will accept and absorb surface dirt differently than the oil paint. The degree of disparity would depend on just how lean (or thirsty) the ground is as compared to how fat the oil paint. Varnishing the work would diminish the difference, especially as Matthew mentions, if the painting is given multiple coats of varnish.
Glad to hear that you are not varnishing with an alkyd medium 😉