I mean, Holo does make its own. They're just using Offkai as an NA bonus.
Though the likes of Phase, Idol, some of the Brave brands getting together and making their own small corpo con probably would be an idea, and not just because including the last one would make La+ fedpost.
They could even attract friendly indies, similar to how Shigure Ui nonchalantly uses the services of Cover's 3D studio.