Hello,
Regrettably, it is not possible to define notification emails only for one particular role. However, you can turn off e-mail notifications in the workflow process in 
Site Manager -> Settings -> Content Management. Then, you can use 
workflow handler to send emails to users of the appropriate role. You can take advantage of several methods (OnAfterPublish, OnAfterReject etc.) and use each of this method to notify only members of one particular role.
Best regards,
Michal Legen