Are Campagnolo and Shimano 11 speed chains interchangeable?
Leonard Zinn has discussed Shimano and Campy 11-speed drivetrain compatibility several times in response to reader questions.

Technical FAQ: Drivetrain compatibility for 10- and 11-speed

Technical FAQ: Follow-up on 10- and 11-speed compatibility

Drivetrain compatibility hidden in plain sight

Although Zinn doesn't specifically address chain compatibility, I'm not sure how you could successfully mix drivetrain components if the chains were incompatible.