The errata states:

You cannot use a Muster Card to muster in a Region occupied by either an enemy army or an enemy control marker, so even if the enemy has left no army in a Region containing a Settlement he has captured from you it is impossible for you to muster there.

Does this apply to the Riders of Theoden card? It doesn't say "muster", it says "recruit". Does that matter? If there's a Companion in a region with a shadow control marker?

Assuming you can't recruit there, if shadow has control of every single settlement in Rohan, can you still recruit if there is a Companion in Westemnet? It seems bizarre that you can prevent the Free People from recruiting in places that are recruitment places but can't stop them from recruiting in the two Rohan regions that you can't otherwise recruit into.

MadmanAtW said:

Yes, it applies. Muster and recruit are the same. A Companion will not override the restriction.

MadmanAtW said:

You can still use the card in the Fords of Isen or Eastemnet if there's a Companion there, since they aren't Settlements and can't be controlled by the Shadow.

I should also add that the Shadow Player can keep the card from being played in either the Fords of Isen or Eastemnet by simply leaving a single Army unit in each of those territories, as a card muster can't be done in a territory containing an enemy Army.