In my last video
How to rig a character from Blender to UE4 with Uefy Script v1.3 - YouTube](How to rig a character from Blender to UE4 with Ue)
around 32:05 mark I reset the rotations on the lower finger bones. Unfortunately the finger bones on the unreal mannequin are wavy and not straight. So I do this in all of my tutorials. If you plan to make a lot of your own animations then this is definitely the thing to do.
However if you want to mostly use marketplace animations from epic games built on the unreal mannequin. Then it might be better to leave the finger bones as is and fix the mesh instead. Meaning the bones will remain wavy like they are in the mannequin. But you will go into edit mode on the mesh and straighten out the finger mesh instead.
I expect most people will use the script with prebuilt animations and only create new animations to fill in any blanks or custom needs. It is unfortunate that the fingers are wavy in the original mannequin. We just have to work around this issue based on the needs of the project.