Central Repository is just another SQLWATCH database, the same requirements and principles apply. Although any existing SQLWATCH database can become central repository at any point in time it is recommended to have it on a dedicated host due to the potential workload and performance overhead as it will be downloading data from the remote SQLWATCH databases into the central location.
The Central Repository Server will also be monitored locally, in the same way as any other SQLWATCH deployment.
Data collection from remote instances can be done with SSIS or by using Linked Server.
SSIS Package is used to download data from remote SQLWATCH databases.
The Central Repository database does not have to be hosted on the SSIS server, in other words, there can be dedicated SQL Server hosting the central repository and one or more dedicated SSIS Servers.