The pariah gene within the Human Race is a very important gene for the forces of the imperium that fight the forces of the warp, rogue psykers etc.
Are there any examples of other species having their own version of Blanks or is this solely a human phenomenon?
TLDR
So to be a blank your race must have a connection to the warp. This cuts out the majority of the races from the possibly of even having blanks. The Orks, Tyranids, and Necrons for sure. The Tau have a very minimal presence in the warp and no psykers, however, they are relatively young and could just not have enough of a presence yet. As they evolve, just as humans, it is possible they will gain more and more of a presence in the warp. Still, as they have a minimal presence it is possible they already have blanks, but just don't know/care yet.
All that really leaves is the Eldar. Regarding blanks I don't think there is a clear indication of whether or not the Solitaires fall into that category or not. For humanity, a blank is someone who has no connection to the warp. Having a connection to the warp is also considered as having a soul; i.e. Blanks have no soul. Solitaires fall into this category, but I believe they have been retconned (I have no official sources).
Originally they were Harlequins that lost their souls as opposed to never having them in the first place. Today I believe they are identified as still having their souls, but pledging them to Slannesh upon their deaths. Though this is is basically what happens to all Eldar that do not wear a spirit stone as I understand it...
Either way, just as human blanks Solitaires are shunned in their society, make others feel uneasy, and are unaffected by psyker abilities. Solitaires check all the boxes that a typical blank would require, but even prior to the retcon it wasn't official they could be labeled as blanks...
I think humans are special in this regard...
