Wasn't Dr Marco a sacrifice?
From the Full Metal Alchemist Wiki:


  Knowing this, the Crystal Alchemist attacks Envy using his hidden transmutation circle to critically damage the Homunculus' core stone. 


Knowing this, he likely has not seen the truth. And as such, would not have been a sacrifice, right away.

However, it's not unreasonable to think that the homunculi may have forced him to see the truth once they were ready, (similar to Mustang.)