The series resistor could be also considered as source side termination for the open ended transmission line between oscillator and uC, particularly if the trace has some length. We are generally using it for fast single ended CMOS signals to prevent multiple reflections running back and forth the line. The resistor also prevents voltage overshoot at the far end. Ideally the sum of oscillator output impedance and resistor should match the trace impedance of e.g. 60 to 70 ohm.
If we observe radiated emissions due non-optimal ground return for the clock signal, a stronger filtering of the clock could be considered. With a well chosen ferrite bead, the waveform can be even changed to quasi sine wave which would be still accepted by the uC clock input.