I looks like it's set up to share vacuum between the hydrovac and the axle. Is it just the "exhaust" from the axle's vacuum diaphram that come to the tee and then to the breather in the cab? If not, if they're actually sharing vacuum, it doesn't seem like an ideal setup to me. There is a reservoir of vacuum in the brake unit that is reduced every time you shift the axle. If the axle diaphram, hose or vacuum switch springs a leak you will lose breaking force. It might be worthwhile to install an extra vacuum tank and separate the two systems. I did this and used an air tank from a semi trailer that had appropriate mounts. I bought is new and it wasn't expensive. Be sure to use a check valve between the manifold and tank.
