Poettering: The Biggest Myths

Of course the HA manager needs to monitor the HA services, systemd doesn't provide a mechanism for running monitoring scripts, but it doesn't have to maintain a parent/child relationship with them when sufficient tools are provided to reliably start and stop the daemon. That way you can take advantage of cgroups and all the kernel features that are trivially exposed by systemd (man systemd.exec) without duplicating all that code, probably less reliably, in your HA system.

If you aren't using clusters for HA with inter-server failover than systemd does provide several critical features for making a local service highly available such as automatic restarts (Restart=on-failure), hardware watchdog support and a protocol that a daemon can use to be watchdogged by systemd (man systemd.service, I think you can just use systemd-notify --status="WATCHDOG=1"), should one wish to add support for it to their daemon.