As a member of the Imperial Yeomanry, he would have spent a lot of his time protecting the lines of communications, escorting convoys of supplies etc, freeing up the regular soldiers for more soldierly pursuits. Few histories have been written about the many companies that comprises the IY so it is probably not recorded anywhere what he actually did.
Not sure if you have your Great Uncle's medal rolls? I have enclosed them for your records.
His Queens South Africa roll has Thomas serving with 31st company where he was attached to the machine gun section. Clasp entitlement Cape Colony & Orange Free State. His Kings South Africa medal was issued with him serving in the 115th Sharpshooters.
You only live once, but if you do it right, once is enough.