One of the issues with using some of the more popular source controls systems out there (e.g., Subversion, CVS) from PowerBuilder is that PowerBuilder uses MSSCCI (Microsoft Source Code Control Interface). MSSCCI was originally developed as a common API for source code control systems, but later abandoned it as they moved to Team Foundation Server. Older source control systems (e.g., Serena PVCS) support MSSCCI, but many of the newer ones do not. Even if you want to use Microsoft's Team Foundation Server, you need to obtain a MSSCCI provider that translates the MSSCCI calls into something that TFS understands.
A similar option (a provider that translates MSSCCI calls into something else) is available for some of those other systems though. Historically, PushOK has been a choice for people who wanted to use Subversion or CVS, as PushOK supplied a provider for each. Recently I started researching this issue again because of a pending migration to Subversion, and I discovered Unified SCC, a single provider that not only supports Subversion and CVS but Bazaar as well.
Will update as work progresses, but so far it's looking good.