Flying business class should get you access based on class of service.
https://www.fijiairways.com/en-us/ex...remier-lounge/
But does not list "Finnair Airways Business Class Guests", but has "Complimentary use for Fiji Airways Business Class guests"

Which airline "tickets" is irrelevant. All based on class of travel and flight number (~ if codeshare)
Master thread of sorts --> Question on Fiji Airway mixed cabin lounge access
For others is a very complicated table for lounge access.

To me FJ as "Oneworld connect" has little value, but a lot of confusion.
Better if FJ became a full member or reverted back direct freq flyer partnerships -arrangements with individual airlines