I just conceded a game against a ghost and finished in 1st place. My final 1st place opponent, during/after the previous turn, conceded or lost to a ghost. Rather than risk losing to a ghost myself, I played through the tavern and conceded before my turn ended, finishing 1st.
If I don’t concede and lose to a ghost in such a situation, do I still get 1st place?
Does conceding lower my rating gain?
I have bit trouble seeing the situation here.
Conceding before playing the round and getting kicked out by losing that round,can lower your rating gain in some situations i think. Because it will place you below a player who get kicked out during the round. While if you play the round and get kicked out together with another player you will share places. (about this i am not 100% sure i have to admit).
If there is 2 players left. And your opponent resigns before the round starts (for example because he think he will lose anyway). The game will sometimes still cue that round (against the ghost at 2nd place).
You dont have to concede in that situation to get first. You will still be first if you play that round and lose it.
Conceding in this situation has no effect on your rating. But it might have an effect on the rating gain in the first situation that i described in my post. Because you will end up with for example a 5th place instead of a shared 4th/5th place.
You see it just fine 
If you are the only player left alive in the lobby you will always get first place even if you lose your fight against the ghost or concede. You can actually concede before the combat even starts in the buying phase and you will still win. Conceding doesn’t have any effect on your rank or your mmr lost or gained, it is the exact same as losing normally or getting first vs a ghost.