Currently with "wide links = no" server denies access to files that are symlinks pointing to files within another share.
According to wide links documentation from smb.conf(5):
"Links that point to areas within the directory tree exported by the server are always allowed"
My reading is that if target file is exported then symlink must work.
Of course that would be slightly insecure (bypassing share level access control) so I guess that paragraph should actually be:
"Links that point to areas within the same share are always allowed".
However, since symlinks to paths in another share are actually useful and security impact is very small and configuration dependent, I would like to request additional option like "wide links = share" that would allow such behavior and still be compatible with "unix extensions = on".