So, if the god Mars is Nergal, and Nergal is the deified Nimrod, and Nimrod is Orion, then Mars is Orion.
In that case, the meaning of Antares — or Anti-Ares, aka the Rival of Mars — may instead refer to Antares as the Rival of Orion. We could equally say “Anti-Ares” means “opponent to Mars (aka Orion)” in the sense that the star is opposite Orion in the sky. That Antares, the alpha star of Scorpius, is a rival to both the alpha star of Orion and the planet Mars enhances the notion of these opposing forces.
These conjectures represent a vastly simplified version of the complex mythologies surrounding the origins of these ancient constellations. But further support may come from the myriad myths and legends surrounding the battles between Orion and the Scorpion and why they lie opposite one another in the sky.
One such link dates to ancient Egypt, where Orion represented as the sky god Horus in a boat. Mars, too, was depicted as Horus. In the sky, Horus lies opposite Osiris (the constellation we call Scorpius), the god of death and rebirth. When Horus rises, Osiris sets and slips into the underworld. The cycle represented how, in life, the pharaoh was Horus, while in death he became Osiris.
By the way, it just may be ironic that Orion is the spacecraft NASA plans to carry humans to Mars. As always, send your thoughts to sjomeara31@gmail.com.