The newest SP36 version of GaBi is not (yet) compatible with the regular openLCA LCIA method package (as stated in the GaBi 2018 in openLCA documentation). Currently, this makes it tricky to combine both databases. As of now, you would need to build your own LCIA methods to achieve compatibility.
We opted for this approach as we wanted to release the newest GaBi version as soon as possible but we do plan to release another version that is in a line with the usual openLCA reference data ... this will then allow to combine both databases and use the normal openLCA LCIA method.