I need to configure KDM as a XDMCP client, I have gotten this to work by setting loginmode=remoteonly or defaultremote... But I the get the greeter where I have to select a server... is it possible to autoselect a server in this dialog???

My distribution is RHEL6 with KDE 4.3.4

Based on a quick analysis of the code, i'm afraid this is not possible - you cannot pre-select a given server, nor can you pre-fill the manual input field.