A significant amount of the Irish Volunteers weapons were from Germany. Erskine Childers landed guns from Germany in Howth, North of Dublin, in 1914. Roger Casement spent time in Germany trying to recruit Irish POWs and buying more arms. A shipment was intercepted off the South coast of Ireland on Good Friday 1916, the ship known as the Aud was German but disguised as Norwegian. The ship was scuttled when they were caught. Casement himself had arrived via U-boat a few days earlier and also got captured, and ultimately tried for treason and executed.

There were no German troops, but presumably some German agents active in Dublin, and the crew of the Aud were German. So no direct support, just arms and ammunition the bulk of which never arrived and probably would have been late anyway.

The failure of the Aud to land the weapons led to the leader of the Volunteers, Eoin MacNeill calling off all activity for Easter Sunday, this is the main reason the rising was predominantly confined to Dublin.

*edit by "no direct support" I mean no military intervention.