Sure - the volunteer RE units supplied detachments to serve with regular companies. No more than 50-115 served from each unit, the Royal Mons had 257 who served.
Apart from their small numbers issued, the joy of these units is that they are named to "R.E." - just like the regulars. From memory the only volunteer units not named RE are the Royal Monmouth Militia (but not all, I have a medal with the unit as RL: ENGINEERS.), Anglesey Militia and Electrical Engineers.
Many years ago, 1977 to be exact, I acquired a QSA clasps Cape Colony, Laing's Nek, Belfast and SA1901 engraved to "Lieut W.J.Hely, R.E. Vols." Research conducted later indicated Lt. Heley was in charge of a section from 1st Sussex Volunteers. I no longer have Lt. Heley's medal and I don't think I ever saw another engraved/impressed to "R.E.Vols".