I know this is a few years late and a dead topic, but here is the solution.
1. In terminal disable to hidden library folder: (you need to do this to browse to the folder)
sudo chflags nohidden /Library/ ~/Library/
2.Copy the obse files directly to /"username"/library/playonmac/wineprefix/TheElderscrolls4_oblivion/drive_c/Program Files/Bethesda Softworks/Oblivion
3. Open playonmac, Highlight oblivion and choose "Configure" on the Left side in the option menu
4. Go to the miscellaneous Tab
5. Then choose the option: Run a .exe file in the virtual drive, And navigate to the Oblivion folder where you dropped the OBSE files, NOTE: Make sure the OBSE_loader.exe is in the same directory as oblivion.exe, and all the other OBSE files.
Run the Exe and this should then work.
You may want to create a shortcut, but I haven't done this yet. I am opening obse_loader.exe every time I want to play oblivion and have not taken the time to see if I can create a shortcut for this.
I updated this forum post as I have not found another post anywhere on the net fixing this problem. I have seen others having the same issue on various wine forums.
Note: I have not confirmed mods using obse work. But it should. I will try to update this post once I can confrim, But I might not update this post even after confriming on my own, just as a disclaimer.
This should be similar to playonLinux as well
cheers and good luck.
Edited by bigben932