Could I as the LS player, play Yub! Yub! and Focus an Ewok controlled by the DS player to remove a DS Emhancement?  The card just says 'Focus an Ewok' but not one of your own.  Conversely, Focusing other players controlled cards must be wrong or you could use their Enhancements or Objectives.  It is sneaky but I feel it is illegal.  Cheers!

The DS would never have an Ewok. The DS capturing a card does not mean they control it or can use it. Captured cards are just captured cards and are blank in all other respects.  Page 26. 

Capture and Rescue
Some card effects instruct the DS player to capture
a card. Only LS cards can be captured. This is done
by attaching the captured card facedown to the DS
objective designated in the effect’s text. If no DS
objective is specified, the DS player may choose which of
his objectives the captured card is attached to.
When a card is captured, discard all its tokens,
enhancements, and return its Force card (if any) to its
owner’s supply. A captured card has no characteristics
(i.e. no text, type, numbers, or other information), and
is considered solely a captured card until rescued or
discarded.

Also the controller of a card can focus them not the other player. Page 10.

A card’s controller may focus a card to perform
an ability or take some other action. When doing
so, a focus token is placed on the card.

There is a card that allows the taking control of an enemy unit.  It may be just character or Droid, but I don't have the game with me.  I am pretty sure it is 'take control' and not 'capture'.  The more I think about it, the more I believe my instinct of it being illegal, is correct.  Cheers!

Rashley said:

Not familiar with this card, but, even in that instance, you could not use the ability since you no longer control said Ewok.

I searched the list on CardGameDB and I didn't see anything come up that allows you to take control of an opponent's card.  Although the repeated use of "unit you control" does imply that ability will be in the game eventually.  So while I won't say the Dark Side will never be able to have Ewoks on its side, they currently can't.

Better anser:  TO implies a cost you cannot use a card you do not comtrol to pay a cost with an enemy card