In the new dev branch (4.21), the google ARCore provide a new API to get the camera image ([FONT=courier new]GoogleARCoreCameraImage). Unfortunately, there are nothing to get it as a 2DTexture. There are [FONT=courier new]GetPlaneData (not exposed to Blueprint) that return an array of uint8 
Why the UE version doesn’t expose camera image such as the Unity API?
Is it plane to add this feature?
From memory you can use the ARCore camera feed as a texture in the material - there is a material function node for that called “GoogleARCore Passthrough Camera”
So to make things clear, the GoogleARCoreCameraImage object is used to provide image bytes access on the CPU side. The GoogleARCore plugin currently doesn’t provide a way to access the passthrough camera texture. That GoogleARCore Passthrough Camera material node could give you a texture but it may not synced with the camera. We are working on adding the support in future release.