For them to win? Nothing short of a miracle. Are we talking 300 PE only? Or are they supporting the 2.5k soldiers already stationed in Helm's Deep?
Supporting the humans they would actually put up a decent fight, maybe even destroy all the explosives and war machines since the magick users can launch fire at em.
The archers would do great with their powerful bows, and the melee types... not so much. Uruk-Hai were kinda ridiculous on that end.
"There is no room for mistakes today, my children. For as I have been told today is the day I die. I'm sorry I never played the part of your father, and from the looks on your faces, it seems that's all you've ever asked of me. It is time for you to go into these worlds alone, with all of my love. I'm sorry, I love you all so very much. Now become what you were meant to be. Become hell."