[Raynor]

In a draft letter, Tolkien noted:

Originally Posted by Letter #244

Until much had been done by the restored King, the Prince of Ithilien would be the resident march-warden of Gondor, in its main eastward outpost – and also would have many duties in rehabilitating the lost territory, and clearing it of outlaws and orc-remnants, not to speak of the dreadful vale of Minas Ithil (Morgul).

Therefore, at least these "lost territories" would be cleared of orcs.

Originally Posted by Kuruharan

We don’t know (because we are not told) how much of a strain it would be for a Vala to control the will of another being.

Tolkien did speculate in HoME X:

Originally Posted by Orcs, Myths Transformed

In any case the number of orks that were thus 'absorbed' was always only a small part of their total. To hold them in absolute servitude required a great expense of will. Morgoth though in origin possessed of vast power was finite; and it was this expenditure upon the orks, and still more upon the other far more formidable creatures in his service, that in the event so dissipated his powers of mind that Morgoth's overthrow became possible. Thus the greater part of the orks, though under his orders and the dark shadow of their fear of him, were only intermittently objects of his immediate thought and concern, and while that was removed they relapsed into independence and became conscious of their hatred of him and his tyranny.