it works you just have to add the UENUM() macro to the enum to forward declare it in ufunctions
Working simple version of the project with forward declarations and enum isolation:
EnumFDec.zip (8.5 KB)
You can regenerate it and it compiles zero errors
compile output
Mockup enum
Forward declare
Then include of the enum file
And if i make it blueprint callable here it is in the editor 
