What I've seen at number of hawker centers (higher end after recent remodeling) they started accepting NETS FP, but it is still unpopular with merchants, they claim that system 'does not work'. FP mostly irrelevant for tourists and people visiting short term, because loading FP card would require trip to MRT station and using machine there.

Also there was an article saying that at one hawker center now it is trail of payment using QR codes, but that payment system requires current account at local bank to make payment, so it is NETS's extension. Again, irrelevant to tourists.

TL;DR - if you want to enjoy hawker food - get cash. Also, if you get into Comfort/Premier taxis - ask them before getting in if credit card is OK.