Yeah, this temp track problem is a haunting one in film soundtracks... However, as William says, the great composer does conform to the director's instructions but makes the temp music his own. Great examples include Jarre's Lawrence of Arabia (Born Free imposed temp track) and Goldsmith's Star Trek I (the whole of Star Wars as a temp track was "politely" imposed, as if anybody could imitate that...).
I must say, one of my very favourite soundtracks is The Secret of NIMH from Goldsmith. One would be illiterate not to see that Debussy was tempd all over that film, but somehow Goldsmith wove his language around it (more or less...), for a uniquely atmospheric soundtrack.
Incidentally -and that's funny- I consider Star Trek II and Aliens Horner's strongest soundtracks (from all Horner films I know), along with Cocoon and Brainstorm. I generally don't like the man's music, and no, I haven't seen Titanic (on principle).