Only 3 went to the gate. All will some form of the truth. One doesn't have a body. The transmutation circle only targeted those people. Marco presumably didn't know anything about the truth. Even with all that truth under the truth crap. He still had to use transmutation circles.
They also used the failure soldiers as sacrifices, making the 3 sent to the gate unharmed, meening there's a use for them there. Technically they have not been 'sacrificed' yet.
However, if your sacrificing something, someone possibly went with them in order to make sure things go smoothly. After all, dude in flask tried to make a gate to there before. As for where I'm going with this... well, I dunno.