You could try setting the hidepid=0 in /etc/fstab just to see what happens. Add this line to /etc/fstab and reboot.
proc /proc proc rw,nosuid,nodev,noexec,relatime,hidepid=0
It would be interesting to see if the problem persists with hidepid actually set to zero.
Running debian 7.8 with the above stanza in /etc/fstab "mount | grep -i proc" does not show hidepid option actually set to 0.
If I set it to 1, then the hidepid option is shown
morgan@debian:~$ mount | grep -i proc
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime,hidepid=1)
However, even with "hidepid=1", and "ps aux" only showing the procesess for the current user, permissions for the /proc/PID directories are still 555 not 500.
root@debian:/proc# mount | grep -i proc
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime,hidepid=1)
root@debian:/proc# ls -al | head
total 4
dr-xr-xr-x 80 root root 0 Jul 26 14:33 .
drwxr-xr-x 23 root root 4096 Jul 26 08:43 ..
dr-xr-xr-x 8 root root 0 Jul 26 14:33 1
dr-xr-xr-x 8 root root 0 Jul 26 14:33 10
dr-xr-xr-x 8 root root 0 Jul 26 14:33 108
dr-xr-xr-x 8 root root 0 Jul 26 14:33 11
dr-xr-xr-x 8 root root 0 Jul 26 14:33 110
dr-xr-xr-x 8 root root 0 Jul 26 14:33 119
dr-xr-xr-x 8 root root 0 Jul 26 14:33 12
A similar question was asked here, for ubuntu 10.04
http://ubuntuforums.org/showthread.php?t=2173093
However, even running ubuntu 10.04 with kernel 2.6, the /proc/PID permissions were still 555, not 500.