The Alliance wasnt that foolish to go in the deadly swamps, where the draenei were hiding.
However a few draenei have helped them a little. But if Alliance found the draenei, their united forces would easily defeat the Horde, and maybe even stop Nerzhul from opening the portals. And in my Afterstorm idea, after Nerzhul was defeated, and Horde was slowly defeating the Alliance Expedition, draenei came out of the swamps and their combined forces have pulled the Horde back, and even had destroyed a part of it.