So is Ultimate Longshot not Longshot, since he is a Mutant from Genosha rather than a genetically created entity in an alternate Universe. The same goes for Mojo, I can't imaging the Ultimate Mojo being the emperor of an entire dimension, but he is still ultimately the same character.
Ultimate Colossus was a Russian Mafia strongman, rather than a farmer in soviet russia. Ultimate Nightcrawler was trained and abused by Weapon X, as opposed to having been trained and loved back in his old circus. Ultimate Storm was never the goddess of any African tribes I am aware of. Ultimate Dazzler was/is a smalltime Rock Icon, and far more of a drunk, smoking type of character than her counterpart. Ultimate Ultimate Gwen Stacy came from a broken household. Ultimate Norman Osborn was commisioned to create the OZ serum that led both to the creation of U Spiderman and the U Green Goblin by the US Government. Ultimate Captain America kills like any other soldier, and never faced the trauma of the death of his young partner, Bucky. Ultimate Nick Fury earned his rank in Operation Desert Storm. Ultimate Hulk was an attempt to recreate Captain America, and was initially an injection to force transformation. Ultimate Thor is a Left-winged radical (not meant in a derrogatory way at all) and spent the early part of his life as a patient in a psychiatric hospital (rather than as a surgeon). For pete's sake, Ultimate Nazis are big f--king lizard aliens! Despite ALL of this, they are ALL still the characters they were written to be. They've gone through situations to make their characters pretty close to what they are down at the core. The Point of the Ultimate Universe is to get to the Core of characters without ever having to worry about decades of continuity, right? I acknowledge that they're trying to show a more realistic Superhero world, fitting in today's society, but really I think the main point is to avoid that crappy background no new reader has the energy to work out.
Making Cable unrelated to Cyclops doesn't compromise his character, and I also want to say that if Scott and Jean have a child, Rachel would be the most obvious choice, she can utilize an extent of Pheonix's powers without being a part of the Pheonix Force, she is pretty damn powerful. Moreso than Cable, in any case.
Cable, when it is down to the basics, is a soldier who has been fighting wars his entire life, both external and internal, and now finds himself awkward and out of place in today's society.
Also, just to bring it up if no one has yet, Cable was -not- supposed to be Cyclops son, he was actually intended to be a much older Cannonball who had come back from the future. A later writer specified it, but Cable never changed, he stayed a soldier. His parentage doesnt matter, especially in a universe completely devoid of something that can clone a full grown human into a full grown human, making it unreasonable to have him made a clone built by sinister's desire for information about the summers sons (of which there is still one unidentified), not to mention the fact that Essex lacks any such interest at all.
DSF = Stubborn as Hell