No, as long as the UID is consistent it will not care whether the user name differs in the container and on Truenas.
Are you using a host path or ixVolume for data storage? I’m guessing a host path and this is just a permissions issue on the dataset.
Edit: Ok I also had the same issue at first using host path, but was able to get it to run. So postgres containers are a little strange with how they expect permissions. We ran into a similar problem with Nextcloud setup, which includes a postgres container. I tried two other ways of setting permissions, which resulted in the app stopping, but this method (which is the same we used for Nextcloud) was successful.
When you create your postgres dataset, do it with POSIX permissions. Click Edit on the Permissions widget then Set ACL. Set the owner to netdata and the group to docker (these correspond to 999:999). Tick the Apply Owner and Apply Group checkboxes and save the ACL. Then deploy the app as normal, using that dataset in your host path for postgres data storage.
Edit 2: Note for future reference, our team is in the process of working on an automatic permissions checkbox that can be applied to postgres db host paths, which should make this process much easier in the near future.