Essentials are possible to use, but if it is not water soluble it can be a problem.  Depending on what's in the essential oil (which does not necessarily connote water-insoluble), it might clog the atty, if it has lots of big biomolecules in it.  Also watch for lung/
throat irritation, and stop it if there is some.  But a nice lemon sage might be really nice, and a nice break from the usual candy flavors.  
I think FlavorArt sells some savories that they claim are ok for 
vaping.