Sorry I don't have a report to give, but I too have had the game crash with Ents and spiders. However, by simply kicking the graphics down from "high" texture quality to "medium" texture quality, plus putting unit detail on "low", I have found the game can play with Ents or spiders and of course Sauron (the bigger the army he commands, including sometimes Mumakil on the same battlefield, the more likely my game will crash).
After such battles are done, I just kick the graphics back up to the way they were before and enjoy the detailed eye candy once more.