Can fstab options uid and gid be the user-group name or must they be numeric?

The Linux mount program interprets non-numeric parameters to uid and gid options as user and group names respectively. This applies to all filesystem types. It works both if the options come from the command line and if they come from /etc/fstab.

Source: source (old (parse_opt), new (mnt_optstr_fix_gid, mnt_optstr_fix_uid)).

If you are using an ext filesystem, the uid and gid options are ignored, as the permissions used are set by the filesystem.

To quote gilles from another answer:

On an ext4 filesystem (like ext2, ext3, and most other unix-originating filesystems), the effective file permissions don't depend on who mounted the filesystem or on mount options, only on the metadata stored within the filesystem.

One method to resolve this would be to chown or chgrp the filesystem at some point when mounted.