YES you need to add thrust if necessary (in most every case) to get the plane to track straight and not pull when you throttle up and down. Flying 3D requires just as much precision control as IMAC or Pattern. You can get away without it sure, but if you want the plane to fly worth a flip then you need to eliminate all the torque and coupling issues and get the plane flying neutral otherwise you will be fighting all sorts of problems.

You need to correct the right thrust issue, you need to find the correct CG so that the plane requires little to no trim to fly straight and level, unless you want to start playing with incidence to counteract the coupling. You need to laterally balance, once you get the CG where you want it you need to mix out the coupling ESPECIALLY if you are flying tail heavy. Tail heavy planes want to fly with the tail down (DOH) so you have to add down trim to get them to fly straight and level. Therefore when you are on knife edge not only does the plane want to pitch to the belly naturally in most cases but it is magnified by the down trim. Thats why its really better to trim a plane for neutral level flight and then just learn to hover the thing that way. Its no harder than with a tail heavy plane once you get it right. If you want the tail heaviness to get more "life" out of the plane, just increase the throws, modify to increase if you must and add more power. I assure you most all planes dont need to be real tail heavy to 3D.
You are almost always going to have roll coupling so if you really want a neutral plane you can mix that out too.

ALL of this will make the plane easier to hover becuase pitch, roll and torque induced yaw all have effect even whlle the plane is not flying because of prop wash and torque that are always present. You get rid of all those bad tendencies and the plane will be a lot easier to deal with.

SO if you want a plane that flys "OK", and you dont mind dealing with it with the sticks then that is fine. A lot of people do it and the better you get, the less you notice the little stuff (except the torque problem).

YES if the plane is pulling then you really do need to add right thrust or a rudder to throttle mix to correct the problem.

If anyone says that this is wrong and real pilots fly without mixes or thrust correction I think I just might stab myself in the head with an icepick.[X(]