Look at the Air Corp's experience of SAR & air ambulance. Up until recently it occupied a lot of the AC's meagre resources & time, to the detriment of military operations and training. The same would be true for the Garda ASU, it would be called off to accidents left, right & centre. The ASU is small unit, it could not perform it's primary mission if it was given an air ambulance role.
On top of that, there's the issue of medical expertise. Who would attend the patient while in flight? Does an EMT do it or would the Gardai? If it's left to the Gardai do they get extra training? Who pays for this training & extra costs?
I'd also say that involving the Gardai would result in the HSE or whoever saying that they needn't fund a dedicated service as someone is already doing it for them.
A proper, dedicated air medical service is what's needed in this case.