Looks like NOT queries are also always handled correctly, even basic ones. Extreme example: the query string
smith NOT smith
gets sent to ES as
"(+(smith) (smith)) AND (ca_objects
and returns all the objects related to smith, instead of none at all.
Unfortunately the quick fix of inserting the "-" in the appropiate line is not enough, there are compounding rewrite issues.
In fact even SqlSearch is not immune, for example searches like smith OR NOT xxx fail to rewrite and all return null in all cases.