Can they both play in the same team?
Grealish plays in the position where Fred (not doing what he does but that would be his best position in my opinion) does in our team if he comes long term - kind of doing the thing that Mctomminay does where he goes on a run with the ball and goes past 2 or 3 players.
Mctomminay does it with strength and power, Grealish can dribble him self out of tight positions, make short passes & find himself out off the press before finding Rashford in acres of space.
I don't see the whole Grealish is a creative passer thing - I see his ability to break a team down in hard situations with his technical abilities before finding a player in a better area to make a pass to.
Maddison is different and more a traditional CAM who will play through balls, play wider balls and take shots from central areas.
I think they could play together but they need a proper hardworking CM or CDM for that to work & Grealish will need to learn how to play LCM before that can happen either.
I'd like to see how Maddison is without Vardy before going for him to be honest - Vardy makes exceptional runs.