Both the ADRF6520 and ADRF6518 have spectral noise density specified in dBV/Hz. It should be dBV/sqrt(Hz). The error has been noted (but not corrected) for the 6518. The same error cropped up in the 6520. It is correct for the ADRF6510 and ADRF6516.
I will add that to the list of changes to the next datasheet revisions of the ADRF6518 and ADRF6520.