Yes, there are several ways to select the group of customers that you would like to email:
Select and email a custom group of customers from the Customers page - simply select which customers you would like to contact from the list then click Actions > Email.
Email all the customers booked in to a session or course by navigating to the session on your schedule or course in the Courses tab, clicking Attendees or Customers respectively, and then Email attendees.
You can also email all the customers with a certain package by going to Packages > select the relevant package > Package customers > Email.
Following the instructions above you can email any customer, whether a main profile or a sub-profile of another customer, and the email address noted on the customer record for that profile will be loaded in to a blank email in your default email program.