Are there any restrictions on how the MBSA detection catalog (WSUSSCN2.CAB) can be used by non-Microsoft tools?
Not directly, but this file is supported when used in conjunction with the public Windows application programming interface (API) provided by Windows Update Agent. The API accepts this file only with a valid digital signature from Microsoft and uses it to perform a scan of the specified computer. Refer to the Windows Server Update Services Software Development Kit (SDK) for details.