You can purchase and place a EMS Command vehicle into a Fire Station with EMS Extension, however you CANNOT send people from a Fire Station with EMS Extension to a EMS School Training course, meaning they cannot receive EMS Command Training.
You also cannot transfer a EMS Command vehicle from a Fire Station with EMS Extension to a Medic Station or Clinic, it will only let you transfer it to other fire stations. The programming appears to treat the EMS Command Vehicle as a fire vehicle HOWEVER...
You CAN purchase the EMS Command Vehicle within a EMS station or clinic...and then from there you can train those people with EMS Command Training.
2 Separate Bugs:
1) Employees within a Fire Station with EMS Extension CANNOT be sent to EMS Academy Courses
2) The EMS Command Vehicle cannot be transferred between a Fire Station with EMS Extension and EMS Stations or Clinics.
P.S. I lost 40K trying to figure out this issue so hopefully it can be fixed to prevent others from being confused