Playing with the latest nightly build of Blender from Blender Builds - blender.org and I discovered that it’s now possible to go round-trip from Blender to UE4 and back to Blender and have it match the original skeleton if you don’t make extensive changes to the skeleton. You can add bones on to the end of a bone chain, but can’t insert bones into an existing chain.
This is a big step forward for Blender. Up until now, I’ve been unable to use the default UE4 HeroTPP_Skeleton because I couldn’t get Blender’s exported FBX to match up.
I think it does, but it’s not completely straightforward. The bones all come the same size and all oriented along the Z axis (Y axis in Blender). This makes skinning a little weird, as you can’t rely on autoskinning unless you resize the bones, and moving or resizing the bones can result in odd results on import. I’m still playing with it and trying to figure out exactly changes you can make to the imported Hero_TPP armature and have it still import properly.
If you search the threads, there’s a thread that has a blender version of the Hero_TPP rig with IK. I’m pretty sure you could use that to create new animations using the nightly build, though.