dns went down and all JMX hosts went into problem state as no data was received. However over ip all hosts where still reachable on the correct port

in the Java gateway log we had this as output:
Caused by: java.rmi.UnknownHostException: Unknown host: omv-services-on-1.vm.cumuli.be; nested exception is:
java.net.UnknownHostException: omv-services-on-1.vm.cumuli.be
at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:616) ~[na:1.8.0_91]
at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:216) ~[na:1.8.0_91]
at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:202) ~[na:1.8.0_91]
at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:130) ~[na:1.8.0_91]
at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:227) ~[na:1.8.0_91]
at java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:179) ~[na:1.8.0_91]
at com.sun.proxy.$Proxy0.newClient(Unknown Source) ~[na:na]
at javax.management.remote.rmi.RMIConnector.getConnection(RMIConnector.java:2430) ~[na:1.8.0_91]
at javax.management.remote.rmi.RMIConnector.connect(RMIConnector.java:308) ~[na:1.8.0_91]
at javax.management.remote.JMXConnectorFactory.connect(JMXConnectorFactory.java:270) ~[na:1.8.0_91]
at com.zabbix.gateway.ZabbixJMXConnectorFactory$1.run(ZabbixJMXConnectorFactory.java:76) ~[zabbix-java-gateway-3.2.1.jar:na]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) ~[na:1.8.0_91]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[na:1.8.0_91]
... 3 common frames omitted
Caused by: java.net.UnknownHostException: omv-services-on-1.vm.cumuli.be
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184) ~[na:1.8.0_91]
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:1.8.0_91]
at java.net.Socket.connect(Socket.java:589) ~[na:1.8.0_91]
at java.net.Socket.connect(Socket.java:538) ~[na:1.8.0_91]
at java.net.Socket.<init>(Socket.java:434) ~[na:1.8.0_91]
at java.net.Socket.<init>(Socket.java:211) ~[na:1.8.0_91]
at sun.rmi.transport.proxy.RMIDirectSocketFactory.createSocket(RMIDirectSocketFactory.java:40) ~[na:1.8.0_91]
at sun.rmi.transport.proxy.RMIMasterSocketFactory.createSocket(RMIMasterSocketFactory.java:148) ~[na:1.8.0_91]
at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:613) ~[na:1.8.0_91]
... 15 common frames omitted

funny thing is that the hostname "omv-services-on-1.vm.cumuli.be" is not used in the zabbix host configuration only the IP so this means that for JMX zabbix still relies on DNS even DNS is not configured in the host.