Integrating various version control systems due to mergers and acquisitions?

Companies acquire other companies that use different version control systems.

Is there a common wisdom on how to integrate such systems together, for example using a Subverson-GIT bridge or even deciding on using just one tool over another - and how to migrate bet开发者_如何学Cween systems?

Do people use a set of criteria for such decision making, for example an equivalent to the "Joel" test on software development?

See: https://softwareengineering.stackexchange.com/questions/24361/method-for-integrating-various-version-control-systems-or-choosing-one-over-othe