I don't think so. I mean, yes, she seems to be nice to Dawn, but that doesn't mean that she is a lesbian. Otherwise, Ash and co. And even JJM would have romantic feelings for every single person/pokemon they have nicely helped.
For the stalking thing (Yes, some people actually THINK she was stalking Dawn), I don't think she was actually stalking her, their meeting each other was nothing more than a coincidence (It's no more stalking Dawn than Gary stalked Ash, which means that they met by coincidence rather than having them follow him/her.), and even IF it turns out that Zoey was stalking Dawn, it doesn't mean that she is a lesbian. Remember, for the most part, JJM stalks Ash and Co. (there have been times where they met by coincidence, but for the most part it was stalking), and they don't have a romantic relationship for any of them (they might have a grudging respect for them, yes, but they don't have a romantic relationship.).
And for those of you who say that she is one since she is a tomboy, just because she is a tomboy doesn't mean that she IS a Lesbian. I mean, need I remind you of Misty? She was a tomboy as well, and the Last time I checked, she was straight. and before you say anything about her not being a true tomboy due to her having girly traits, due to the fact that the Majority of the fans view contests as a girly thing (not that I think that, but still...), Zoey technically has some girlyness in her as well, so she isn't really 100% either.
that's my 2 cents for you all.