I don't know about half, but some part of it - definitely.

I'd also add, that there are some non-trivial requirements for good server daemon programs, like fork, detach from terminal, may be fork again, umask, chdir, may be close some descriptors, maintain PID file, output to syslog, drop privileges and so on. And a lot of those things are implemented in systemd, so basically you can just write very dumb server which will work properly under systemd. So some part of systemd have to be implemented in every server daemon program.