No there are no HCO3- in saliva generally.But there are Cl- ions.

The dissociation is:
NaHCO3-------------Na+ + (HCO3)-

•Na+, K+, Mg2+, Ca2+, SO42-, Cl-, NO3-, HCO3-

anions are negative ions.

•SO42-

•HCO3-

•CO32-

•Cl-

It might be due to Hamburger's effect( chloride shift). In venous blood, RBC will take up CO2 and CO2 react with water to form carbonic acid ( H2CO3). This acid will then dissociate to form hydrogen ion ( H+) and bicarbonate ion (HCO3-). HCO3- will flow out from RBC and each efflux of HCO3- will be accompanied by influx of Cl-. In some circumstances, some HCO3- and Cl- remain in RBC or maybe the rat eof exchange of HCO3- and Cl- is not the same, and this create water flow into RBC, thus volume of RBC will increase (RBC swells) and hence it's hematocrit value too.