Is atmospheric turbulence irrelevant for ExoPlanetary transits and radial velocity measurments?
One can imagine turbulent eddies in atmosphere as very weak optical lenses which focus and defocus stellar radiation. This leads to image degradation (seeing) and fluctuations of flux being registered through some aperture. The latter effect is called scintillations. It is very prominent for naked-eye observations. For telescopes the averaging by large aperture reduces the magnitude of the scintillations. Nevertheless it is main limiting factor for high-precision photometry at telescopes larger than ca. 2 m. See e.g
http://adsabs.harvard.edu/abs/2012MNRAS.426..647K   

As for spectrscopy, atmospheric turbulence does not affect the wavelength of radiation as long as in modern high-precision spectrographs (e.g. HARPS) actual detection takes place in vaccuum.