In regards to the final point, I am checking that TCAS provides RAs regardless of the Mode A setting. We as controllers cannot provide vertical against GA squawking 7000 because we cannot be certain the Mode C is accurate, and A0000 aircraft is definitely producing unreliable SSR data. I don't think TCAS interprets Mode A... however, due to controllers being unable to provide vertical, some of my collegues believe TCAS will do the same and only provide TA against such aircraft.
Sorry for being so confusing haha, and thanks for the replies so far,
Andy