I have 3 adult male Blue Dempseys... one that is aggressive compared to a typical adult JD, one that is about average for an adult JD and one that is docile for an adult JD...
I also have an adult Blue female that is more aggressive than her larger mate... I'm not sure how 'tough' she is, as her male takes care of anything she starts... but she starts confrontation with just about everything I put her with...
I've kept my more aggressive Blue males with Adult Oscars, Adult female GT, Severums, Clown Loaches, Black Ghost Knives, young adult female Trimac, Convicts, female Dempseys (Blue, Gold & Standard), Red Head Geos, Firemouthes and several others...
As juvenals, I baby them keeping them in tanks with no other real competition and with UV lights... as adults I suggest avoiding fish from the Amphil & Parachromis families or other fish that would easily coexist with such fish...
For the simple fact that Adult Blue Dempseys are high dollar / hard to replace fish, I would suggest keeping them as the 'King of the tank'... but if you have other tanks to move trouble makers to then I see no reason not to push the envelope.
Each of my adults were the nicest / strongest of a large group of Juvenals... Blue Dempseys do seem to have a higher percentage of 'runts' than standard Dempseys... but once you have a nice strong male I wouldn't consider them any weaker than standard Dempseys...