I know that there sorta-kinda-but-not-really already is an Ultimate version of the Red Skull, some snot-nosed punk with a Darth Maul lightsaber thing runnin' around calling himself the Colonel, but there needs to be an actual Red Skull to face off against the Ultimates. Maybe put him up with the Ultimate Sons of the Serpent or something.
Anyhoo--
"Corbin Smith, grandson to long-presumed dead Nazi warcriminal Johann Schmidt--an SS agent known in the intelligence community as the Red Skull because of his personal insignia--became enamoured with the legend of his ancestor, and twisted by the glorified tales he had been told by his father, took it upon himself to carry on his grandfather's work, eradicating the 'impure' from the world. He considers himself the true Captain America, since he believes his is the 'true' American Dream. A brilliant tactician, he shows no fear when engaged in combat, even braving the wrath of post-humans such as the Ultimates themselves."