We have tested it in RTK mode with DJI base D-RTK 2 station and it worked well. We have not tried NTRIP connection but app supports it and it seems that this feature
works too.
Just in case, you do not need precise absolute positioning in the world just for mission planning feature to gain from RTK. All you need is ability to exactly follow routes built from initial overhead flight. If both initial and second flights are captured with the same configuration of base station you are fine even there is a constant shift to absolute positioning. This is convenient property when using mobile base station as you don't need to care too much about measuring precise base station coordinates or rely on NTRIP signal strength.