Some of the screenshots of this tutorial are a bit misleading now because the new UE4 mannequin is not in T-Pose any longer but in A-Pose. If you read the full tutorial then you could see some issues with different poses later but if you look on the upper screenshots then it looks like it could work with A-Pose to T-Pose somehow (which actually does not). Seems like the screenshots of the final result are still the old ones (old T-Pose blue guy -> T-Pose squad) and it seems it was a bit easier with T-Pose -> T-Pose with the fingers because if you switch the translation retargeting from animation to skeleton then it usually does not fix issues with weird finger rotations any longer because the chance that the fingers are posed like the UE4 mannequin ones is pretty small.
If you would fix this issue then you have to switch the translation retargeting from animation to skeleton in UE4 and you have to switch the rest pose (in Blender) or the retargeting pose in UE4. If you don’t need the finger animations at all then it’s easier to just skip the retargeting of the fingers (in the advanced tab of the retarget manager). Because it’s way easier to add a tiny modification to the animation starting from the rest pose of the fingers in UE4 than to untwist all those tiny bones.
Makehuman guy - retargeted third person anim (without fixed rest pose - but already with retargeting translation set to skeleton):
Makehuman guy - retargeted third person anim (without fixed rest pose - but skipped fingers in retargeting manager):
Retargeted again but fixed the rest pose in Blender a bit previously (just quick for screenshot):
Edit: Usually the closer you get your rest pose in Blender to look like the rest pose of the UE4 manneqin the better the result afterwards.