Just did my stay at conrad singapore and shangri-la hotels singapore. Here's what I found,
I needed 2 rooms at both hotels.
Conrad singapore I booked 1 room for 2 nights with hotel collections to get the bonus $75USD + 1 category upgrade, the $$ was a little cheaper compared to booking directly. Issue is the total amount was charged automatically at checkout or checkin (not sure but was marked as prepaid by the hotel systems) so I could only get 1 statement credit. Diamond status was recognised.
For the other room I booked directly with the hotel, managed to split payments to 2 cards by paying off $400 on the first night then the rest on the 2nd night.
Shangri-la Hotels
Booked 2 rooms with the 2 nights get 1 free FHR promotion, came to $2253AUD, was able to split to 4 cards at $500 each by paying off $500 per room on night 1 and night 2 at the front desk. At checkout used 5th card to pay the remainder which tipped us over to get a 5th cashback.
Only had Jade status with shangri-la, did get a room upgrade for both rooms but it was just a "view" upgrade which means nothing to me. Kids enjoyed the pool and their buffet breakfast was much better than conrad's.