So there’s probably a bit of clarification that needs to be made around that plugin—it’s a community plugin that I’ve forked with the intent of enabling it for Sensu Go usage (see https://github.com/sensu-plugins/sensu-plugins-systemd/pull/15). So that said, while my name is on the plugin for bonsai, it’s really more of a test to ensure that the plugin and the changes I’ve made to it enable it to work with Sensu Go.
I’m not aware of a plugin that’s specifically for sysvinit/upstart systems that would monitor services in the same way that this particular plugin does. And frankly, there’s a plugin that might actually be better to use for this sort of thing: https://bonsai.sensu.io/assets/ncr-devops-platform/nagiosfoundation. This collection does contain a process & service check and happens to be cross platform for Windows/Linux. It doesn’t have the Ruby runtime dependency either.
However, if you find that you do need something for CentOS 6 and feel like writing something for it, the Sensu community/maintainers are always open to contributions.