[jdbburg]

Not a stupid question. However, I think that this process (whether it is included in calculations or not) shouldn't contribute to the dark matter issue. Electrons and positrons are "normal" matter and if they are anywhere near e.g. a star, they will contribute to the plasma around the star and therefore be visible. Also, even if it were not visible, my intuition is that the process is too rare to produce enough mass to account for the dark matter