I'm not sure if this helps or not but a common way of monitoring "What" gets installed is to use alerting/monitoring. The following document will outline on how to do this at least with Add/Remove Program applications. You will basically receive an alert that can be sent to an email each time an application is added or removed from the monitored device. It's not quite reporting and more on the real-time side of things but I thought I would bring it up in case it helps.
You might try using the ProductComputer.EntryDate column (introduced in 9.5 or 9.5 sp1) to determine what products have been installed in the last month. Software - Products don't detect every piece of software installed but it does get most so this might work for you. Just join that with your list of administrators and you have your report.