The FBX->DAE conversion is sometimes problematic. With 2.74, I find it’s better to use the FBX import in Blender. You can’t export back out and have it match the Epic skeleton, though - even if you add a root bone, there’s still an issue with bone orientation that causes the animations to not work.
Instead, I import all the animations I want into Blender and then re-export them all and use that instead of the stock Epic skeleton. Minor one-time hassle to convert stuff over to Blender, but pretty minor.