This is a common mistake. systemd-oomd is not "in" systemd the init system. Similar to systemd-resolved, systemd-networkd, systemd-boot, and others it just has the systemd name because it is developed by the systemd team. A minimal system using sytemd for the init system and other software for everything else only needs sytemd, dbus, and journald.
I use several of these projects because I like the systemd design philosophy (ex the way the CLI interface and config files are) and trust the developers of their software. However, there are popular altenatives available for all of these components, should you choose to use them:
systemd-resolved: bind9, dnsmasq, powerdns
systemd-networkd: NetworkManager, ConnMan
systemd-boot: GRUB2, Refind, EFISTUB
systemd-oomd: earlyoom, nohang, oomd (the facebook one, not systemd)