I don't believe there is an event defined for tools installation as you mentioned, when you right click on a powered on VM and do a tools installation it's calling - MountToolsInstaller which does not return any value back for you to monitor. It most likely generates a task in which you can probably search the system and trigger of off that, but nothing in real time at least default from the vSphere API.
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William Lam
VMware vExpert 2009
VMware ESX/ESXi scripts and resources at:
VMware Code Central - Scripts/Sample code for Developers and Administrators
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