Tell Me
Yes. By default your "From" address will be your Kerberos username (e.g. username@umbc.edu).If you would like to send mail using one or more of your custom UMBC email aliases (e.g. FirstName.LastName@umbc.edu) then you need to use the Google account tools in Gmail. You can manage your custom UMBC email alias from Webadmin.
Follow the steps, it will send you a confirmation mail to the requested "send mail as" address that you entered. Since it delivers to your mail box it will actually show up in your UMBC Gmail account, you click approve, and then you will have a drop down option when you compose messages that will let you send as a given mail address.
Google has some help on this topic at http://support.google.com/mail/bin/answer.py?hl=en&answer=22370&ctx=mail