Huh, that's completely bizarre. I didn't realize the Vashar couldn't be druids.
In fact I almost think a mistake was made. The "creation myth" of the vashar talks about the first vashar being killed by the gods, then resurrected by a demon, and creating the rest of the races through the womb of the demon. And yet, in the same line that says they're never druids, it also says they're never members of the Thrall and Disciple PrCs, or Bards or Barbarians.
And almost none of that line makes no sense. weird.
I don't know, a case could be made for vashar doing a lot of things they supposedly "never" do, like the fact that clerics don't have to worship gods, but could instead represent causes or philosophies (it wouldn't even be particularly weird to see a cleric of deicide).
It's ultimately up to you. I see no reason why a vashar couldn't be a druid, as long as he's not worshiping anything (which isn't technically required), but that's me. Failing a druid, I'd probably go with wizard or sorcerer.
hm, a thought occurs, (though it somewhat cuts down on some things I had in mind...) what about a ...bug druid, thing. I think the WotC website's entomancy articles talked about bug druids, or at least swarms as animal companions, but never gave this kind of druid a name.
Like I said, it's up to you. I tend to debate for what I want, but if you say that you can't see a vasharan being a druid, I'll go with it.