OK, I finally got it to work tonight!
I think you need .NET 3.5 .NET4.0 and .NET4.5 installed.
I think you also need directx9, vcrun2010 and vcrun3013 installed.
Use the standard xpad with the xbox360 controller., don't worry about xboxdrv. It'll probably work with xboxdrv but I had success with xpad so I can't tell if that's an issue or not yet. Make sure that works first. Use jstest-gtk to check.
Grab the 32 or 64 bit xbox360ce.exe file from here depending on your container type. I stuck with 32 bit. Put the exe in a new folder in the c drive.
Now in PLayOnLinux go to the Steam bottle configuration and under Miscellaneous select Run a .exe file in this virtual drive.
Find the x360ce.exe and run it. When it pops up it'll complain about no xinput1_3.dll. Just click on create to create the file. Then it'll install a couple of xbox controller drivers. Once that is done you can auto fill the controller in the panel and you should see alll the appropriate controlls working. Once you're happy with it hit save and close the panel.
Now just copy the 3 files into your rocket league folder (Binaries/Win32) and it should work!
Let me know if you have no luck and I'll do a full tutorial.