If a person already has a MemberHub (MH) profile in another PTA/school but not your school, MH will send them an email notifying they have been added into a new site. (They should be aware of how MemberHub works as they are a current user, so alerting them should not be an issue - more of a verification.)
However, if this is the first time the person is entered into MH then MH will not notify them. The reason being everyone handles their new member communications differently. For example, if you imported a large email list, you would not want the system to notify everyone until you have had a chance to explain MemberHub and how your PTA will be using it.
Also, the system will email a receipt to the purchaser which will include set-up instructions as well as receipt of their membership purchase and any donation..
If the Membership Chair wants to notify those they have added, they are able to send a customized welcome message to the new members once entered. To do this, go to the People tab and select the individuals they have just entered. Then click Send a Message from the People Actions menu that appears in the grey bar. They will be able to customize whatever message they would like to send.
Additional help on sending messages can be found here.