Absolutely. That's what it's for: passengers in transit between incoming and outgoing flights.

The unknown is if you can check in the night before your morning flight if you are already in Singapore and not arriving on another flight. Can you check in for your flight very early and then go through passport control and up to the transit hotel?

I guess if they'll let you check in that early, the answer would be yes. But they usually don't have the check-in counters open for each flight that early.

It's not like the US where they have generic check-in counters for all flights. They open dedicated counters for each flight.