I uninstalled it off one system and now when I select the server in the console and pick deploy, nothing happens. I do not get the pop-up box asking for credentials. This happens on the second server currently running 6.5 as well.
Since I have 3 licenses, I tried pushing the agent to a server that has not had any version installed before and it worked properly, the agent installed, it restarted and the console can communicate with it.
All 3 servers are running Windows 2003 Standard SP2.
Of course, if you install the full product on a system, that system can be remotely managed in the same manner as if the agent had been "pushed" to that system originally. You can also use the Security Configuration Tool to restrict who can run the local install of the product, if you'd only like the system to be remotely managed.
I'm confident that it is also possible to perform a manual install of the product locally on a server you'd like to manage, and only install the base "agent" and not the local console/GUI. I'll see if I can find more information on this.