That come under the same part where IIRC medics are allowed to carry stuff like sidearms to protect themselves and their patients?
From what I remember, yes - there was a lot of debate about what counted as a "self defence weapon", as the standard SDWs on vehicles like Mastiff and Ridgback were either .50 Cal Brownings or GMGs, with lighter vehicles also sometimes mounting 7.62mm GPMGs, and with common weapon mounts across multiple platforms, the implications of the strategic decision to put a protected weapon station on a vehicle allowing the mounting of a GPMG leading to a tactical decision to replace the GPMG with a .50 or GMG, and so on. I think there was also some debate about to what extent the international law had been tested on the subject, and what weapons could be mounted on an ambulance whilst still calling the vehicle an ambulance, and when an ambulance would be likely to be in a situation where it would need to defend itself, rather than being defended by other platforms nearby.
Of course there were also some pretty significant design issues - if you look at the protected vehicles that are out there, like Cougar (6x6 or 4x4), RG-31 et al, and imagine them with in an ambulance configuration in the back, which means at least one stretcher berth if not two, plus oxygen bottles, medical equipment and so on... and then try and work out where you can mount a weapon station - that needs to be operated by a gunner - and where that station could possibly go that doesn't involve the gunner standing on either the patient or the medics. There are remote weapon stations out there like the Selex Enforcer or the Kongsberg Protector, but that still means you need space for the electronic gubbins and an associated crew station, and space in ambulances is always, always at a premium. It's really something that would need to be designed into the vehicle to begin with, rather than added to an existing production model. Using a bigger vehicle doesn't make it any easier - if you scale up from a theoretical Cougar-based protected ambulance to something like a Buffalo-based ambulance, then you've got the problem of the medics - a lot of whom seem to be 5th percentile females - having to raise stretchers above head height to get patients into the back of the wagon, which isn't something you can really do... so you then have to look at some kind of winching/lifting mechanism that can be operated under stressful circumstances, and which is also going to need to fit in the back of the wagon along with the weapon station, med equipment, etc, etc.
Someone may go out and design a vehicle that can solve all of these problems, but I suspect it's a problem that's likely to continue to be solved by simply sending escort vehicles out with the ambulances. After all, how often to you have vehicles working in multiples smaller than 2 vehicles?