Batgirl, do you think one has to be born with the ability to play blindfolded, or can one practice enough to achieve a "visual memory" while playing blindfolded?
A Couple of Things

Well, most master-level players can play blindfold. Maybe they became masters partly because they have some innate advanced visual memory - or maybe they developed that abilitiy on their road to Masterland. I sure can't say.

Well, sometimes I have a hard time remembering where my Queen ran off to.....then doesn't return! harhar

I've never heard of that kind of shared blindfold simul before. It sounds even harder than a regular blindfold simul, since Alekhine and Koltanowski had to remember each other's moves, as well as their opponents' moves on all six boards. I'd love to see two modern GMs attempt the same thing!
It's all about patterns and sequences. There's a really good study that I can't remember the source for (Batgirl might know, being a chess historian) about that. In a nutshell, they did a study where non-chess players/amateurs/masters were shown a variety of chessboards with pieces set up, and then had to recreate the positions from memory. In positions where sequences/patterns are likely to occur in play (e.g. a castled position with pawns on f2, f3, and f4, a king on g1 and a rook on f1) then the strong players did much better, but in positions where the location of the pieces was completely arbitrary there was no difference between the chess master and the non-players.
Basically, high-level players develop a great memory for pattern recognition, and I think it's probably this that lets them play blindfold - because they can easily visualise these commonly occurring patterns.

This experiment with "random" and "real" positions was mentioned in one of Garry Kasparov books. If I remember correctly it was 'How Life Imitates Chess"

I'm not a chess historian, but I do know that Alfred Binet (of Stanford Binet IQ test) studied blindfold chess players' memories. His resulting thesis was "Psychologie des Grands Calculateurs et Joueurs d'Échec."
A couple interstig thngs I found looking up something else:
"Chess Review," April 1934
"Chess Review" 1934