From what I have been playing with, no you will need one for each host as the templates like base-metrics and icinga2-influxdb-host will adjust the panelID depending on the dynamically generated list of services.
Take, for example, panelID 34 for my switch is a different panelID 34 for one of my servers. If I am reading the way this works correctly, then choosing something that is say, Load at panel 34 for my switch may actually be Procs for my server depending on the number of services on the server.
That said, I'm still going to test this theory out unless someone can immediately tell me I'm wrong
There is no panelid34 in base-metrics that is provided with the module. I think you use the icinga2-default dashboard or a dashboard from somewhere else.
If you want support please post your /etc/icingaweb2/modules/grafana/config.ini and graph.ini, and if you have downloaded/created a dashboard, please provide it also.