Can I use GitHub / GitLab / Bitbucket / SVN or other Source Code Manager (SCM) tools as a repository with Deployment Manager?
Ans: Github, BitBucket, SVN and other SCM tools do not makes sense as a repository for Deployment Manager deploying Pega applications.
If you are thinking of using an SCM tool as a version control for rules, that is simply not supported. Pega uses the layer cake concept and ruleset versioning (in the database) and rule resolution as the source control mechanism and that is what you have to rely on.
Once you export the application archive (zip file) that contains the deployable application, you should then use a artifact repository such as S3 or JFrog Artifactory or even the Filesystem to store the artifact.
This artifact is then used to publish to higher environments. All those repository types are supported by Pega, and other artifact management repository can be supported by following implementing the custom repository type as mentioned above.
The Releases feature of Github could be a possible solution, for which a custom repository implementation is needed, but the source control mechanism is not suited for Pega.