Rizwan Saheb,
As far as I know there are no open source monitoring tools that colaborate with HP Loadrunner.
The HP Loadrunner controller offers already a lot of monitoring options.
Per example: you can monitor Windows system from the controller through Windows WMI.
If you have a controller under support at HP, then you may also use HP SiteScope for Loadrunner free of charge.
Per controller you can aquire 2000 HP SiteScope for Loadrunner monitoring points for free.
With HP SiteScope for Loadrunner you are able to monitor Linux, Weblogic etc.
You see a lot of options available.