I've had no issues.
Can't recall off hand if there is any major difference in set up as I don't have anything in front of me but yes, definitely playable with the expansion.
There is nothing written, so that is the reason why I'm asking in the first place.
House ruling to put characters such as Gothmog, the Treebeard, Elrond or Galadriel into play could potentially tremendously shift the balance.
In the rules for the "Breaking of the Fellowship" with the First edition + expansion, The Balrog is dead and his Event Card removed from the game.
Some things can, I guess, be naturally assumed. For example since Gollum is the guide, the Smeagol-related cards (three of them, if I recall) are removed from the game, as well as all Smeagol tiles from the hunt pool.