Anyone had success with SNMP and reboot required state

Should be a pretty easy one to do with SSH. https://megamorf.gitlab.io/2019/06/10/check-if-reboot-is-required-after-installing-linux-updates/ I'd suggest doing it as a property source so you can just put them into a group based on the property. Something like this (not extensively tested). 

import com.jcraft.jsch.JSch
import com.santaba.agent.util.Settings

host = hostProps.get("system.hostname")
user = hostProps.get("ssh.user")
pass = hostProps.get("ssh.pass")
port = hostProps.get("ssh.port")?.toInteger() ?: 22
cert = hostProps.get("ssh.cert") ?: '~/.ssh/id_rsa'
timeout = 15000 // timeout in milliseconds
try {
    def command = 'test -f /var/run/reboot-required && echo needed'
    def command_output = getCommandOutput(command)
    println("pending.reboot=" + command_output)
    return 0
}
catch (Exception e) {println "Unexpected Exception : " + e;return 1;}

/**
 * Helper method which handles creating JSCH session and executing commands
 * @return
 */
def getCommandOutput(String input_command) {
    try {
        // instantiate JSCH object.
        jsch = new JSch()
        // do we have an user and no pass ?
        if (user && !pass) {
            // Yes, so lets try connecting via cert.
            jsch.addIdentity(cert)
        }
        // create session.
        session = jsch.getSession(user, host, port)
        // given we are running non-interactively, we will automatically accept new host keys.
        session.setConfig("StrictHostKeyChecking", "no");
        String authMethod = Settings.getSetting(Settings.SSH_PREFEREDAUTHENTICATION, Settings.DEFAULT_SSH_PREFEREDAUTHENTICATION);
        session.setConfig("PreferredAuthentications", authMethod);
        // set session timeout, in milliseconds.
        session.setTimeout(timeout)
        // is host configured with a user & password?
        if (pass) {
            // set password.
            session.setPassword(pass);
        }
        // connect
        session.connect()
        // execute command.
        channel = session.openChannel("exec")
        channel.setCommand(input_command)
        // collect command output.
        def commandOutput = channel.getInputStream()
        channel.connect()
        def output = commandOutput.text;
        // disconnect
        channel.disconnect()
        return output
    }
    catch (Exception e) {e.printStackTrace()}
    // ensure we disconnect the session.
    finally {session.disconnect()}
}

If you want alerts, you could alert off this property pretty easily with a companion datasource that looks like this:

return 0

With an appliesto like this:

auto.pending.reboot == "needed"