OP here. I did query this with Hilton and they eventually replied with this link:
https://www.hilton.com/en/brands/sma...nd-conditions/
It's spelt out clearly enough:
ACCRUAL OF POINTS
Hilton Honors members will receive base points and elite tier bonuses on the room rate only at SLH. Hilton Honors members will not earn Hilton Honors Points at SLH properties for any other non-room rate “eligible folio charges” as defined in the Hilton Honors Terms and Conditions.