Everyone involved with Prometheus are still walking the "Oh, it's totally not a prequel to Alien" line despite all the early promo images and teaser trailer screaming at our faces otherwise. As long as it's a good movie, that's all that matters at the end of the day.
While continuing with that narrative, helmer Ridley Scott tells the Hungarian site Mozinezo (and transcribed by AvP Galaxy) what role Guy Pearce will play in the not-an-Alien prequel-but-really-it-is:
"When the first Alien movie and Blade Runner were made, I thought that in the near future the world will be owned by large companies. This is why we have the Tyrell Corporation in Blade Runner, and Weyland-Yutani in Alien. They sent the Nostromo spaceship.
The Prometheus is owned by an entrepreneur called Peter Weyland, and is played by Guy Pearce. That’s the connection between the two films, and nothing more. Prometheus is a new film, a new world, and is full of new ideas. And of course new monsters as well."