Likely, not many
It's a poor term of art. The vehicle may not have any emissions (besides water), but chances are pretty good the power it is using did. Better off calling them what they are, or just saying 'vehicles not directly powered by internal combustion engines".
Unless, of course, we manage to come up with a way to use algae/microbes to produce hydrocarbons on an industrial scale, then an IC engine could be 'zero-net-emissions'.