Charlz, 599 Trumpeter HR Shawlders, 78th Battery, RFA is listed on the Queen's South Africa (QSA) Medal roll for the 78th Battery, RFA (Ref WO 100/143 pg 97, dated 10 May 1905) as having been awarded the QSA with Cape Colony, Orange Free state, Transvaal, South Africa 1901, & south Africa 1902 clasps. It is noted that the medal had not been issued on any previous application so it seems this is the only application for him and that he didn't receive a King's South Africa (KSA) medal.
I can find no other men by the name of Shawlders. The only men by the name Shalders that are listed on the QSA roll are an A and E Shalders of the 4th New Zealand Mounted Rifles; a H Shalders in the 1st ILH; and a W Shalders in the Kimberley TG.
The Tpr H Shalders listed in the Natal 1906 roll was with the Transvaal Mounted Rifles. The 1906 Zulu Rebellion was a colonial affair and Imperial troops weren't used to my knowledge. I'm not aware of any RHA or RFA men being detached for service in the TMR but stand under correction. Perhaps another member could confirm this. So unless he left the British Army and enlisted in the [colonial] TMR I would very much doubt it was him. I have no idea if TMR enlistment papers or records survive for 1906.
Cheers,
Mark