Unfortunately the onOverlap events are not able to output any collision information.
There is a work around solution but is quite a hack: You can use onHit events and disable the contact forces generated in physX. Therefore you get the FHitResult (contact normals, contact points etc), while the objects overlap.
As you can probably tell this can only be achieved in C++. You also have to alter the engine’s source files. What’s awesome is that UE4 is truly open! The sky is the limit! and the time of course ;). If you can afford to dig that deep look at collision filtering and contact modification in physX: https://developer.nvidia.com/sites/default/files/akamai/physx/Manual/Callbacks.html