Pipers and Drummers continue to wear their distinctive "battalion tartans" (which used to be their regimental tartans), per the new RRS uniform regs:

Pipers and Drummers
Pipers and Drummers are to wear antecedent
uniform in No.1 and No.2 Dress but are to
comply with these Regulations in all other
orders of dress. They are to wear Regimental
stable belt and tartan patch on Tam O Shanter.

For the whole of the uniform regs:

http://www.army.mod.uk/documents/gen..._Rulations.pdf

Cordially,

David