I did some testing and the bottom ports are indeed vents.
I connected a vacuum pump and power supply and found that they transfer vacuum proportional to current. 600ma (.6amp) delivers full vacuum and is very linear in between 0 and 600ma.

The reason that I wanted to know this is because I am going to design a pressure to current module to operate the waste gate. The system as designed will not let you disconnect the EGR and keep normal turbo boost.