I'm sure that the official stance would be that it's not safe, but that doesn't necessarily mean that it'll be right - vaping is generally seen as smoking in all but name, and I've seen qualified medics on telly suggest that the passive inhalation of vapour is bad, even though there's no scientific evidence of it (and plenty to the contrary).
My gut feeling is that there will be minimal or no risk to vaping while pregnant, but I doubt an ill-informed GP will say that.
Certainly, vaping will be far safer than smoking