USkeletalMeshComponent::LineTraceComponent does not properly consider bEnablePerPolyCollision. It appears to use the component's bodies, which are empty. It should be sufficient to use UPrimitiveComponent::LineTraceComponent instead in this case.
Place the mannequin in the level.
Set the mannequin's skeletal mesh component and skeletal mesh asset to enable per poly collision.
Perform a scene line trace passing through the mannequin's fingertips. (UWorld::LineTraceSingleByChannel)
Perform the same trace, but as a component trace. (USkeletalMeshComponent::LineTraceComponent)
Expected: Assuming no other assets are in the way, the results should match.
Result: The component trace doesn't detect any hits.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-70652 in the post.