It is possible to get to Horde Inn as an alliance if you start under the Violet Hold bridge.
Step 1. Use Dk Path of Frost or Elixir of Water Walking.
Step 2. Swim under the bridge leading to the entrance of Violet Hold and face Dalaran, but just under the ledge, if you're too far in you'll just mount through the bridge. You want the short-wall as head space. Jump until you're standing on the water under the bridge.
Start
To Here
What You Should See
Mount Up and Fly Up Under the Bubble
To Horde Areas
Behind Blue Wall, Bonus Parachute Glitch
Human Infront of Horde Fireplace
Step 3. Mount on something smaller than a Mammoth. I use a Mechanostider. Mount, move forward and jump. You might have to do the mount-jump with 4.0.1; since they f'ed up mounting through walls.
Step 4. once you're under the bridge there are LOTS of places to go. You'll need a flying mount(which will work under the bridge).
4a: Obviously, you can come up under the weekly raid questgiver and stand on the platform with him. Useless, but people have no clue how you got in there.
4b: if you're careful you can get into the walled off enclosure with the dragon in it behind the weekly quest giver. This one takes a little practice and you have to come in from above and the side.
4c: The Horde Inn. If you mount up and head toward the area of Dalaran that has the flightmaster you'll notice a small square cutout on the left side of the flight platform area. Fly toward that from the edge of the water (the short edge, not the long one under the dragon-enclosure deal. You'll come out in the sewers if you don't). You'll come out the wall of Horde inn's kitchen. You won't get transported back out of the area unless you get too close to the door; upstairs is good.
This spot under the bridge is ripe for getting into anywhere in Dalaran.
Happy Exploring.
If this is a repost then the original poster should have included better search terms. If some nerd doesn't spas about reposts then I'll post pics.