Comment 52 for bug 1186662

The /etc/apparmor.d/usr.sbin.dhcpd profile in 16.04 includes the line:

  /var/lib/dhcp/dhcpd{,6}.leases* lrw,

So there should be no issue with manipulation of the leases file.

The systemd unit in 16.04 also includes a 'chown' command to ensure the right ownership of the leases file, so there should be no need for any dac override.

Are you somehow running an Ubuntu 16.04 system with upstart as the init instead of systemd? This is what the user in https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1543794/comments/8 appears to have, and this is not supported.