Yes. To add an activity for an Account Executive go to Actions>Add an Activity. Once the window opens type in all the information that pertains to the activity you are adding. When you get to the Assign To section, be sure to put the name of the Account Executive that you are adding the activity for there. This will ensure that the activity will be assigned to them. Then click Save.
Note: Be sure to uncheck Download to my Calendar. This feature is only for adding an activity for and Account Executive within Matrix. There is not a way to save it to their Outlook, Gmail, or any other personal emails.