The g'mara in B'rachot 5b relates the story of R. Chuna, who seemed to be being punished for something (his wine soured).  It was suggested that he had failed to pay a share-holder, to which he replied that said person had stolen from him.  They cite a proverb that "if you steal from a thief you also have a taste of it".  The g'mara relates that he pledged to pay and his vinegar became wine again.

This seems to be a case of not only stealing from a thief but stealing one's own property back from a thief.  So no, theft doesn't become ok if the target is a thief or the cause is just.