Your first picture of Conan and Valeria in the arena could be a publicity shot, but it looks a lot like a real scene. Note Arnold's positioning, it's exactly from the movie scene, but in the movie we only get to see very little of what is going on and only a little bit of action and gore. Both Conan and Valeria could have fought a group of fighters and they were the last people standing, only ones left in the arena. Or that shot could have been right before the fight. If it was a publicity shot, wouldn't Sandahl have been closer to Arnold or, at least, be looking at the camera? By her checking her weapons also leads me to believe she was being arrogant and just preparing for the fight, while Conan stands ready to coming fighters. There also isn't any blood on Conan yet. If you watch the scene that costume is featured in, he gets very bloody in it and the camera is only focused on him in a close-up, so we can't tell what's going on in the background. From what I gathered, Conan saw her fight in the pits when he was there fighting. The two characters briefly met. So that could have been it. And there was a cut piece of dialogue where she reflects on her life and bears a scar on her neck (from a collar), being that she fought as a slave and gladiator. She won her freedom long ago, but found herself still fighting for money and sport, to prove herself and that she was better than most men. This part was to have taken place in the hut tent when they make love and she tells Conan a little bit about her life. Remember also when Arnold sees her in the garden entrance, he recognizes her and she does him "You're no guard" and "Neither are you" parts. This indicates a prior meeting between the two characters at some point earlier in the film.
According to this guy, the pit-fighter scene was in a flash back sequence. I think he got this from the novelization. There were a few unused flash backs that were in the script and not in the movie, but they belonged to Arnold.
From what I read, the gladiator sequence was to run over 10-15 minutes, we got less than 5 minutes I think. It was all edited to hell, so I guess we'll never know for sure? Sucks! It's funny though that pit-fighter costume was used a hell of a lot for most of Valeria's photos and publicity shots, but never seen in the movie!
The Marvel comic book adaptation has some really nice photos. On the last page, on the inside back cover, there's a shot of Conan chopping at some big hairy guy's neck with the axe. You barely see this in the movie. The guy Conan is fighting looks a lot like Ox Baker, the gladiator who fought Kurt Russell in ESCAPE FROM NEW YORK (great movie, shitty ass sequel).