You can build this in one of two ways in ITSI through KPI's:
1) Use the Data Model option when creating a new KPI, or
2) Use the AdHoc Search option and specifically build your KPI on a search that utilizes your Unix/Linux Add-on data
Hope this helps!
Please create a service using configure option in ITSI and select the existing OS data model as KPI . This will add all the OS related KPI to the Service and you can either choose a Glass Table or Service analyzer screen to monitor.