I don't think it's an addon package, looks to be part of the debian systemd install. You might be able to disable it, though when I do a service --status-all it doesn't appear to be listed.
so does timesyncd use ntp? ntp always seems a bit overly complex to me. I just want all the servers to have the same time. Right now i just have ntp installed and configured through puppet (before I knew that timesyncd was being used on proxmox) and set to to public ntp servers and a very basic conf http://pastie.org/10619933. I have not configured anything special with timesyncd. Just comes with proxmox i guess. Anyway, check_mk is complaining all the time about no suitable peers or timeout/ntp daemon not running, etc. http://www.screencast.com/t/Nb9tM3i8IlAS. i have a mix of Debian 8 (Proxmox servers), Ubuntu 14.04 LTS and CentOS 7. i actually do have two Ubuntu 12.04 LTS systems, but i'm planning to upgrade them.