from ftp-client:
debug_mode is on, and debug_announce is on. When in this mode, you'll see the DEBUG: lines in client window.

[23:06:50] [R] site rescan --dir=/site/incoming/games/../../../../site/groups/test
[23:06:50] [R] 200- DEBUG: rescan: PZS-NG (rescan v2) v1.0.X.r2172 debug log.
[23:06:51] [R] 200- DEBUG: rescan: Allocating memory for variables
[23:06:51] [R] 200- PZS-NG Rescan v1.0.4.r2149: Rescanning /site/incoming/games/../../../../site/groups/test
[23:06:51] [R] 200- PZS-NG Rescan v1.0.4.r2149: Rescanning in QUICK mode.
[23:06:51] [R] 200- PZS-NG Rescan v1.0.4.r2149: Use --help for options.
[23:06:51] [R] 200- 
[23:06:51] [R] 200- DEBUG: rescan: Dir matched with nocheck_dirs, or is not in the zip/sfv/group-dirs
[23:06:51] [R] 200- DEBUG: rescan: Freeing memory, and exiting
[23:06:51] [R] 200 Error executing command.


We then cwd to /groups/test and try to rescan w/o args:

[23:09:25] [R] site rescan
[23:09:25] [R] 200- DEBUG: rescan: PZS-NG (rescan v2) v1.0.X.r2172 debug log.
[23:09:25] [R] 200- DEBUG: rescan: Allocating memory for variables
[23:09:25] [R] 200- PZS-NG Rescan v1.0.4.r2149: Rescanning in QUICK mode.
[23:09:25] [R] 200- PZS-NG Rescan v1.0.4.r2149: Use --help for options.
[23:09:25] [R] 200- 
[23:09:25] [R] 200- DEBUG: buffer_paths: g->l.path=/site/groups/test
[23:09:25] [R] 200- DEBUG: getrelname():        subc:                0
[23:09:25] [R] 200- DEBUG:                         path[0]:        groups
[23:09:25] [R] 200- DEBUG:                         path[1]:        test
[23:09:25] [R] 200- DEBUG:                         g->l_path:        test
[23:09:25] [R] 200- DEBUG:                         link_source:        /site/groups/test
[23:09:25] [R] 200- DEBUG:                         link_target:        test
[23:09:25] [R] 200- DEBUG: rescan: Creating directory to store racedata in
[23:09:25] [R] 200- Rescanning files...
[23:09:25] [R] 200-  Passed : 0
[23:09:25] [R] 200-  Failed : 0
[23:09:25] [R] 200-  Missing: 0
[23:09:25] [R] 200-   Total : 0
[23:09:25] [R] 200 Command Successful.

The same will happen from shell - you are unable to scan group-dirs even if you're root.