How can I determine whether this is a "rail to rail" opamp from its datasheet?
Try this: -



For a power rail of +/- 15 volts the input common mode range is only guaranteed to be +/- 11 volts.

For a light load on the output pin (10 kohm) the output is only guaranteed to swing +/- 12 volts.

An R2R op-amp will never output swing completely to the rails but you could expect it to get within 100 mV on a light load.

Conclusion - this op-amp is NOT an R2R device.