Hmm, it seems that the problem is in CameraRaw.dll file.
I spent a hour with experimenting and found relatively easy solution. I edited CameraRaw.dll file in Lightroom's installation directory with a hex editor (I used PSPad) and switched E-M5 with E-P5 (replaced two occurences of E-P5 with E-M5 and also E-M5 with E-P5). This works! Photoshop now treats my E-M5 photos as taken with E-P5 and allows me to use entire 4:3 area for crops! Also exported JPGs have E-M5 as camera in EXIF correctly.
It seems this forum is dead...
This forum is not dead. There are 100s of messages a day. You seemed to have figured out how to deal with your images, yourself, using a hex editor, and have already rejected the Adobe-supplied workaround of using the DNG Recover-Edges plug-in.
About the only thing to add is why things are the way they are: the way things are working is how they were designed to work at the time the camera models were released.
The issue is that newer cameras can have both the in-camera-specified-crop and original-crop selected in LR, so both the 3:2 and 4:3 aspect ratios selected in your example. Older cameras, before Adobe added this capability are stuck with the in-camera-specified-crop with the possibility of using the Recover Edges plug-in.
Despite the order you acquired them, the E-M5 is actually a year older (2012) than your previous E-MP5 (2013) and the older camera that is newer to you, doesn't have the two crop options available.
I remember Adobe being asked at the time if there was anything that could be done with the older cameras' photos to give them Original-Crop ability and Adobe said it was too complicated to change how cropping worked for already imported images so they weren't going to attempt to do anything.
Possible solutions to your crop problem:
1. Shoot in 4:3 (full sensor data) and then crop in LR - I don't get why not doing this and create problems for yourself.
2. Use Olympus software to reset crop to full sensor data before importing to LR
3. Convert to DNG and use DNG Recover Edges.