I believe the Scarlet Man and the Great Engineer are two people, even though they both carry an Aether lamp.
Aether lamp theory:
Matthew 5:14-15New International Version (NIV)
14 “You are the light of the world. A town built on a hill cannot be hidden. 15 Neither do people light a lamp and put it under a bowl. Instead they put it on its stand, and it gives light to everyone in the house.
I'm thinking that the Aether lamp is a symbol of our -- as Christians -- light. Our light shines in the world and shows people that we are Christians. In the same way, Aether is gained when we do "good deeds" for the Resistance. So maybe the Great Engineer and the Scarlet Man both carry Aether lamps as a reference?
Scarlet Man and Great Engineer theory:
2 John 3New International Version (NIV)
3 Grace, mercy and peace from God the Father and from Jesus Christ, the Father’s Son, will be with us in truth and love.
Allegorically (as it relates to the Bible) Jesus is God's son. Does this mean that the Great Engineer is the Scarlet Man's father?
I have a feeling that these questions and more will be answered in future episodes!