No integration for GIT or other version control has been built into Launch at this point. Since it is API driven, It's definitely possible. However, it's not on the near-term road map. If this is something you'd like to suggest, I'd definitely, encourage you to submit a feature request on the official Launch - Feature Requests community.
In the meantime, you could set up self hosting. This would allow you to direct your various build libraries into your own version control process. Adobe would just pass the library file where you direct us and the version control would be up to you.
The DTM API is only to be used with the AEM integration. The DTM team never planed on releasing a full API for customer use.
Launch, on the other hand, is built in an API first approach where customers will be able to write their own extensions to access Launch and it's APIs. To learn more, visit our Launch, by Adobe community.