In fact, I’m a huge proponent of designing your code around the data, rather than the other way around, and I think it’s one of the reasons git has been fairly successful (*).
So it’s easy enough to just write whatever Java code or something to just access the databases yourself. The object model of git may be smart, but it’s neither proprietary nor patented. I suspect it’s often a lot easier to integrate git into other projects that way, rather than try to actually port the code itself.
(*) I will, in fact, claim that the difference between a bad programmer and a good one is whether he considers his code or his data structures more important. Bad programmers worry about the code. Good programmers worry about data structures and their relationships.