Other than railroad guns and their associated cars, I'm not aware of any at all. Most tracked, half-tracked vehicle's tracks are far wider than even the 5' Russian gauge--they would straddle even the widest rails. Smaller vehicles--jeeps, command cars and the like--were of simple design. Easy to manufacture in large numbers.
Moreover, military vehicles are generally designed to be adaptable to available terrain, and not just terrain with roads. Meaning muddy ground in most cases, and fitting RR track wheels would make negotiating terrain like that even harder than it already is/was. A lot more weight, increased drag (if you've ever tried to drive, tow--or winch--even 4WD vehicles through deep mud you'll appreciate the term "drag," I think).
There are probably exceptions though...and someone here can perhaps educate both of us.