Differential Op-Amp Input Voltage
The input over-voltage section (page 17) in the data sheet says this: -


  If inputs are subject to overvoltage, appropriate series resistors
  should be inserted to limit the diode current to less than 5 mA
  maximum.


Given that you are worried about protecting against over-voltage, the input resistors (R1 and R2) may be subject to a voltage difference of 5 volts - 3.3 volts = 1.7 volts. So, providing that R1 and R2 have a resistance of not less than 340 ohms you will be fine even if R3 and R4 went open circuit.


  My question is if the schematic below safe, in the sense that the
  inputs of the op-amps will not see voltages higher than VCC-0.3V.


I believe you meant VCC + 0.3 volts.