CM,
I agree that a MATZ is class G airspace and I like your overall thinking regarding the service provided.
However, considering your theory regarding the midair;
IMHO;
1. For IFR flights, they are required to comply with approach control instructions from the time they enter the area of responsibility until such time as the flight is clear of the area and no longer requires a service.
2. VFR flights will never be in IMC
3. When in VMC all flights are required to see and avoid.
4. An ATC clearance is issued in respect of Known Traffic only. i.e. Oxford apprach can clear an aircraft for an NDB approach. If that aircraft has a midair with a VFR guy doing aerobatics non-radio in the letdown area then there can be no blame on the ATCO provided that they had no knowledge of the other aircraft's presence.
So if we compare Oxford (Class G airspace with ATC and IFR procedures) and a Military airfield with exactly the same plus a MATZ, really, what is there to stop a pilot from simply telling the controller what they are doing and requesting an FIS while they do it.
As to levels of service mentioned early on, as far as I am aware, a FIS and Alerting service are provided to every flight in contact with ATS. Thus when the controller says "Flight Information service", I read that back not to confirm that I am getting what everyone gets but to confirm that I am not under any higher form of service.
Regards,
DFC