User blog comment:Sppople/Doctor Doom vs Ultron (Comics)/@comment-26395956-20150704130630/@comment-5795750-20150705135745

As far as I've discerned the two have interacted not as enemies but as allies. Let's see if I can quote the Marvel Database to see where these interactions were:

Ultron-11 was re-created by the Beyonder to battle alongside other villains during the Secret Wars. Ultron freaked out because of all the humans around it. He started blasting the other villains. Doctor Doom had Molecule Man ram Ultron into Galactus. Galactus levitated Ultron up to his eye level. Galactus snuffed the power in Ultron and he crashed to the floor. Doctor Doom rebuffed leadership to pursue the Beyonder's power. He found Ultron and reprograms him to follow his commands. After introducing Ultron to Titania and Volcana Doctor Doom instructed him and Doctor Octopus to ready assault vehicles. Doom attacked the heroes' base with their ship, where Ultron attacked...

Blah blah blah... essentially Ultron and Dr Doom interacted during the original Secret Wars crossover

Ultron-13 was rebuilt by Doctor Doom with all of its other body's memories, and as an unforeseen consequence had all thirteen personalities running in its mind at once.

Ultron was rebuilt by Doom and kept imprisoned after completing a mission with the Kingpin.

OK those might have been the only two times but still, Dr Doom and Ultron interacted. Also isn't it highly discouraged to have two warriors from the same universe fight each other?