For completeness here is the response I sent to Simon before I noticed he had created this post on the forum:
------------------------------------------------------------------------------
A Websphere Cell is made up of a Deployment Manager and a number of nodes – the Deployment Manager acts as a single administration point for the nodes within the cell.
In the Websphere Probe terminology the Deployment Manager is referred to as the Administration Node and it is this server that the probe needs to be pointed at. Note that the probe does not need to be installed on the Deployment Manager server although it can be (depends on the OS version) – the probe will discover all nodes that make up the cell and probe configuration allows you to specify which ones you want to monitor.
SF Case 13096 (https://na4.salesforce.com/50060000003KbZw?srPos=2&srKp=00a) is interesting. According to Berbee’s Websphere expert the Deployment Manager can be configured to act as a single access point for all PMI (performance monitoring infrastructure) data from all nodes within the cell. This means you only need to monitor the one server to get performance data for all the others.
--------------------------------------------------------
Ray