I haven't done a lot down in the Darrans but, based on that limited experience, I would expect that in March you could, barring recent snowfalls, head across the sloping benches below Moir's mate and the little brother towards Moir without needing crampons. I wore walking shoes to the Bowen-Allen corner in January a few years ago, for example.
Similarly, if you use the low traverse to Adelaide Saddle to avoid the summit of Barrier Knob, you should be able to get there and to Sabre (and down from the col which is the standard descent) hardly standing on snow at all. We glissaded down from the col in sandshoes but there is a fair chance that in March you might have harder conditions. I expect, however, that it wouldn't be hard for very far and you could figure out a way around if conditions did catch you out.
Accessing the Barrier Knob routes, I imagine you could get in from beneath ok, because you don't have to go right up the Knob. If you want to rap in you will need to climb the snowslope the extends from above Gertrude Saddle to the ridge. In December I just timed my climbing to be able to kick my way up in while chopping a handful of steps. I don't know whether it melts right out, which would be easy, or strips back to ice where you would probably want a pair of insteps.