I don’t know why the answer would be “no,” but if you load a mission plan from Mission Planner into your flight controller, it WILL account for the fact that height AGL is… not perfectly flat in the real world, right?
What I mean is if I tell it to fly 50 meters AGL and it encounters a 20 meter uphill grade on its flight path, the drone will adjust accordingly yes? Or is it something I need to be aware of if I’m making a long, linear path?
depends how you program the mission
by default,
alts are relative to your home altitude.
ie home + 50, for the entire flight
there is also terrain, this is the mode that will try to keep 50m above the terrain based on the srtm dataset
then there is ASL/global - which you would provide the entire flight altitudes in above sea level values.
Thanks! 
If I end up having to program a long, linear mission, I’d rather my machine didn’t run itself into the side of a gradual up-slope.
When you are on the planning screen, right click on the map, and in the menu go to Map Tools → Elevation Graph. It’s a good double check for any potential issues.