Dikembe still has his place as a defensive specialist, with his HoF Def Stopper and Rim Protector and Chase Down. Also his much better Vertical and higher Block.
But I think it's hard to imagine that DI Gasol wouldn't produce more for you, overall. Obviously, he has the elite shooting and elite Post Control and Post Fade. He also has elite passing for a big, elite Draw Foul and Free Throw.
And even just on D, he's +14 on Strength, and +12 Steal. For perimeter D, he's +5 Lat Quickness, and +6 Acceleration. He might be as good a defender, overall. And he's massively better, offensively.
Finally: if this is for your starting slot, Dikembe only has 85 Stamina. Gasol has 97.