Sure, but with the treaty they cannot go nearer than 6 hexes to a town.
That would be a ring of 42 hexes to watch around each city.
Covering each of those hexes around Spacerock with say 2 Archons each
would require 84 Archons.
That seems a lot, given around 600 Archons to cover all of Erf.
Also, more scouts means more chances of them being spotted,
and CC might not have wanted that, for the duration of the treaty.