Just in case someone is reading this thread and looking for the answer, here it is:
No leave is required to proceed on an HHT. Period. The member is considered on duty and the block in Monitor Mass has an option for putting a soldier on HHT. The HHT request form which goes through the member's CoC is usually kept (in copy) at the OR and as a Tp WO I kept copies as well in their shadow files.
I know this because we banged our heads for weeks last year attempting to come up with the right leave type. Our CO would not authorize special because there IS no special for HHT found anywhere in the CF Leave Manual. We were forced to figure this one out. Reading CBIs, CFAOs and Relocation Services Manual in conjunction with TB, the determination made was that HHT was duty much like TD. When a member proceeds on TD he/she is not on leave.
Hopefully this clears it up for future "lookers into-ers"!!