I just figured out a pretty easy way to do it using only DS and UE. Once you get the bone-bone relationship figured out for the rigging, it’s just a matter of creating a pose in DS that matches the UE4 default skeleton, the A-Pose I believe. It’s a lot easier this way because you can dial in each pose position using the float fields rather than guessing with the 3d gizmo in the UE Editor, so you can be a lot more precise. I just exported the UE4 mannequin into 3d studio and kept changing the pose and exporting/importing (merging) it into the UE4 scene until I had it all matched up. I’ll write a tutorial and post all of the values when I get a chance. I still need to tweak it a little bit on the fingers.
Once you have your pose exactly like the UE4 mannequin, then do a File->Save As and save it as a Pose Preset. Now any time you create a character in DS, just add that pose before you export. One thing to note here… I already had a pose preset from iClone for all of the face morphs so I had to apply that first, then lock down the head and apply the A pose to the body. It was the only way to use both poses on the same figure.
Now just export your character with the A pose as an fbx with the morphs (I used 2012 binary) and drag it right into the UE4 Editor (I’m using 4.16). Let it create a skeleton and be sure you import the morphs, etc. Then just create the rig. I’ll post the reference to that as well. In my case, “Genesis3Male” was my root node.
Once you’ve created the rig, you can retarget an animation and when it’s done, open up the animation (it’s going to be ugly at first) and at the very bottom-right corner of the Skeleton Tree tab, select the drop-down and check the top option, “Show Retargeting Options”. Then right-click on the root node (again, “Genesis3Male” in my case) and select “Recursively Set Translation Retargeting Skeleton”. That should clean it up.
Of course, you only have to create the rig once. After that, just create more DS characters, apply the A pose and import it into UE4 using the original DAZ3D skeleton.
EDIT: This didn’t work. I got them perfectly lined up and the DAZ character doesn’t look natural at all, arms too long, shoulders too far back, hands too big, and even though the hands are exactly the same on both sides, the fingers on one hand are still mangled. I’m not sure what’s going on there. The animations themselves look fine but the UE skeleton doesn’t appear to be ideal for matching up human characters, at least not the grey one. The old blue guy seemed better.