We're not using UE3. UE comes with the mod tools baked into the engine. It's handy when releasing editing tools. But not every engine works that way.
We use a variety of tools to setup our levels for playthrough. the video linked above really only takes into account the art side of level creation. It doesn't account for design, onslaught setups, or putting in trap grids (definitions of where traps can be placed). While we've greatly improved our internal tools to allow us to do things better and faster for game development, creating a whole toolset that we can release to the public as a downloadable individual program would still be a hefty amount of work. As an independent studio, we need to stay focused on creating games, our primary product. Shipping free editors takes a ton of resources, and while it would be a brilliant addition to our community, it ultimately isn't going to keep the studio running on it's own.
We recognize that this game is a great fit for some mod tools. We hope to add the onslaught editor we had in OMD1 back in for this game, but we won't be supporting full level creation at this time.