Yes. Once a custom background is uploaded, it is available in all of the Studios across the Production for all participants who join from the Riverside website. Team members and guests can also upload their own custom backgrounds to the Production.
Please note that if someone joins a studio from the MacOS or mobile app, they cannot see the custom backgrounds uploaded to a studio. However, they can add their own custom background.
Likewise, if you upload a custom background to a studio from the Riverside MacOS or mobile app, it will only be available to you. Team members and participants who join your studio will not be able to see it.