Leeway in selecting Inductors
There's no general answer to your question.  There are lots of factors to consider when selecting an inductor (e.g. ESR, saturation current, interwinding capacitance, lossiness including core and AC losses, etc.).

I wouldn't consider 9.9nH to be "in the ballpark" of 0.6nH as it's more than a decade higher in inductance.  In this case, it seems like more inductance would be better at filtering the power supply, but if there are supply transients drawn by the part the higher inductance could lead to higher ringing and overshoot so it would be best to go with the inductance specified in the datasheet.

I'm surprised that they don't give more information about acceptable inductors in the datasheet, because the type of inductor can have a big impact on performance.  I would expect that a lossy inductor (maybe a ferrite bead) would be preferred in this application, but again no guidance in the datasheet.  I would check to see what they use on the evaluation board for the part and go with that since you know that it has been tested.