For me nuget seems the best option.
But in general here are my 2 cents.
1- If the LLBLGen generated code is only maintained by one team, and all the rest are just consumers, then a dedicated repo for it only accessible to the team in charge, and the consumers should use nuget to access the appropriate version.
2- Otherwise the build script of the consuming projects can reference a dependency on a folder where the DAL artifact is published.
3- If all the applications are in the same repo (using different branches), then another branch for the DAL would be good enough.
P.S. I don't recommend having any dlls or builds in the source control.