Hmm, interesting. I can reproduce your results. Thanks.
However, note the following:
[user1]$ chmod g+rx /home/user1
[user1]$ touch file; ls -l file
-rw-r--r--. 1 user1 users 0 Jul 26 15:24 file
[user1]$ su user2 -c "ln -s /home/user1/file /var/tmp/link"
[user1]$ ls -l /var/tmp/link
lrwxrwxrwx. 1 user2 users 17 Jul 26 15:26 /var/tmp/link -> /home/user1/file
[user1]$ [[ -f /var/tmp/link ]]; echo $?
1
[user1]$ su user2
[user2]$ [[ -f /var/tmp/link ]]; echo $?
0
Something does not add up.
From experimenting, it appears that only the user who created the symlink will get true for the file test.
Thank you.