A couple of notations. You state:
SQL Mail requires a MAPI profile. As a result, if SQL Mail is to be used, a domain account is necessary.
SQLAgent Mail also requires a MAPI profile. It too requires a domain account in order to be used.
This is incorrect. We are running our SQL Servers with local IDs on the server and are using SQL Mail successfully to notify us via page of any alert conditions. You just have to setup the mail profile on the server under the ID you are using to run BOTH SQLServer and SQLServerAgent.