Hi David,
Yes, it is possible to get to Arendsig from the Masongwana Gorge trail, which is shown on the hiking map. The trail ends at Cambalala House, the MCSA house near Arendsig (the old forestry experiment project forester's house), and there are various vague trails up to Arendsig from Cambalala House. Although it is quite a steep slog up to Arendsig, it isn't difficult, and you can even make your own way up through the grass.
It should also be possible to join to the Organ Pipes trail near the met station from the Masongwana trail south of Cambalala House by a similar slog up the ridge.
I have no idea of the current condition of the Masongwana trail, and it might be worth trying to have a look at it on google earth.
