Hi lotusteve
It would depend on the angle of incline of the surface, a tilt of a few degrees, say 10° would not make significant difference, however as the angle increases the centre of gravity of the drone changes, there will be a point where the CG is so far forward that as the rotors spin up an begin to exert lift the uphill side of the drone ( assuming the orientation of the Home point is in line with the incline) will get lighter than the down hill side, and at the point of take off the drone, it will pivot around the down hill supported leg, and fall over.
It may be possible that exerting maximum lift immediately might " snatch" the drone off the ground but I would not try it, and as happydays says it might even do it as soon as you power up (assuming P3)
Regards
Waylander