How will supply ripple affect OCXO performance?
Edit based on Spehro's answer-  After re-reading the datasheet I think it's correct to say that the 50% is 50% of 50ppb.  My original interpretation doesn't seem like it would be a very practical product.  However, the recommendation for an LDO still seems valid.

I would say based on the wording below in the datasheet that this part is very sensitive to supply variation:

Supply Voltage Variation (measurement referenced to
frequency observed with TA=25°C, Vs varied from 3.13V to
3.47V, VC=1.65V/NC and load=50Ω/15pF): ±50% of frequency
stability

There is likely a frequency dependence to the supply rejection, so we can't assume that the DC rejection ratio applies to switching supply ripple (it could be better or worse) but by extrapolation 20mV*147 %/V = about +/-3% frequency variation.  I'd go with a good low-noise LDO.