I rewatched the "tent" scene.
From the dialogue, Marion seems to differentiate between Belloq and the Nazis.
"What kind of people are these friends of yours?"
She uses his first name, "René". (I believe that the only other person to do so in the film is Indy... and I think that Marion says it first.) Now, could Marion have heard of him from Indy? Sure. (Just not on Sallah's roof, she leaves with the kids/monkey before Indy and Sallah's discussion.) Also, Indy refers to him as "Belloq" with only one exception, so it seems like if Marion knew him from Indy mentioning him, she'd know him as "Belloq". And while we could imagine some sort of introduction happening earlier (Hello, I'm Rene Belloq, and I'll be your captor this evening
)... it seems to me that the tent scene was the first time that Marion and Belloq had run into each other at Tanis. The dialogue seems to indicate that until the tent scene, Marion had been under the Nazi's supervision, not Belloq's.
"I must apologize for their treatment of you."
Finally, there's something about Marion's look in that scene. Yes, there's some coyness. There's something else... to me it looks like an old attraction. In terms of expert confirmation of that... I can only cite my wife (a certified Jane Austen Maniac) as agreeing with me. But I'm sure there are any number of interpretations.
So, again, nothing conclusive... but interesting speculation nonetheless.