They're a group from DC; it's a scifi story, set in the Vega system. The Omega Men are actually an army with some two hundred members, formed to combat the evil Citadel, which had enslaved the Vega system--sort of like Star Wars, really. But only a few of them are important--Primus (one of their leaders; telekinetic powers), Tigorr (Primus's ally, but also a rival for leadership; a cat alien who could turn fully into a gian cat, the last of his kind with that ability), Broot (a giant alien; belongs to a race of pacifists, but was banished because of his violent behavior), Nimbus (a disembodied spirit who kills with a touch), Harpis (a winged being, the victim of experimentation by the Citadel; her wings were ripped of by Lobo's partner, but she later regained them), Felicity (a female of Tigorr's species), Doc (their doctor, cybernetically enhanced), Kalista (Primus's wife), and Shlagen (largely worthless comic relief). The first four on that list are the most important.
The problem was that come Issue 26, the cast changed. Suddenly, and without warning, we were reading about a whole new group of people--the Green Man (a former Green Lantern), Elu (a something surrounded by a forcefield), Ryand'r (Starfire's brother), and Artin (an artificial intelligence). Okay, they still had Tigorr and Kalista with them, and the others eventually showed up, but for the longest time, it was like reading an entirely different comic. Plus, at the same time these people showed up, the readers were thrown into the middle of a convoluted story, so not only did the readers have to deal with a new cast, they had no idea what was going on. This is what I was talking about when I said that the new creative team messed things up.
They're main enemy was named Harry Hokum, and was human. I don't know if he existed in the DCU before Omega Men.
The Omega Men aren't around any more, but they were cool while they lasted.