What is Required to use Oracle Performance Manager to monitor SQL Server?
I think you are probably looking for Oracle Enterprise Manager or OEM as it is normally referred as, a good starting point for more information is here.


a. Oracle database starting with 10G+ do their own data collection (Automatic workload Repository), however, you need to be licensed to access much of that data. You can still use statspack (which is free). OEM actually uses this collected performance metrics and uses them for display via its pages.
b. Live views are available to use (the V$ and GV$) in Oracle, no experience with SQLServer, but I suspect you have similar views available.
c. OEM can send you alerts on events and conditions that exceed user defined thresholds. This is configurable via templates or custom metrics (aka User Defined Metrics).
d. OEM has some performance reporting built-in, but you can use OEM repository to roll your own reports, it is not  very difficult (have done it in the past). OEM repository is simply a different database, the SYSMAN schema contains tables and views which expose all collected data. You can adjust retention, only constrained by available storage. It can provide your historic information as well as realtime performance for Oracle. You will have to check the plug-in for similar capability for SQLServer.

OEM can (with using optional plugins) monitor SQL Server, check this link for a brief overview. In my shop there is no SS, so I don't have first hand experience in using these plugins.
Licensing information for OEM is here, I'd definitely recommend reading this manual to  you and your customers.
There could be, but once you read through the information linked above, you will get a better idea. Then a quick chat with your Oracle Sales team will yield more information as well.
Some of the extension packs for OEM are listed here.


Hope this gives you enough information to get started on it.