Confirmed HSBC cannot use Cardup to earn rebates/rewards. Tried before & asked CSO, they said its a payment service provider so does not qualify.
So far, its only UOB, BOC, SCB to be worthwhile...not sure about OCBC & CIMB.
DBS & HSBC confirmed no.
Maybank Plantinum Visa also recognises the CardUp use for rebates though the rate (3.33%) is lesser than BOC's