Dryer venting options on second floor with gambrel roof
I think Option 1 is your best option, but could you explain what you meant when you said that, "roof vent dampers won't operate at this steep of a pitch."

Are you concerned that they won't open, won't close, or both? A straight 10' run of 150 CFM dryer exhaust won't have any problem opening the damper, if anything you'll have a problem with it staying completely closed when the dryer off.

If you have a problem with it staying closed, then take a galvanized zinc nut and glue it to the vent to hold it down when the dryer is off and to prevent gusts of wind from lifting it. These vents are usually installed around 35 degrees, but yours is at 75 degrees, so you'll want to vent flap to be heavier to stay closed as it will be almost vertical. 

Don't forget to remove the screen mesh from the vent if you're using it for a dryer!