Cellophane will not prevent "marrying" of flavors. Real cello is made of plant emulsion and is therefore quite porous. It allows for air exchange and mostly adds a layer of protection against damage during rigorous storage. It does however slow the process markedly, since flavor exchange occurs mostly in the form of oils passing from cigar to cigar. As air is exchanged by moist gasses escaping from the cigar, since there's not direct contact leaf-to-leaf, it's slowed. There is alway a little bit of oil attached to the gas exchange, so it does happen; just to a far lesser extent.

Naked cigars laying next to/on top of one another is the primary way flavors become exchanged. Over the years, there's been some debate on how extensive this process is. On the extreme end of the debate is Carlito Fuente, who holds that laying cigars of different types together will result in rapid and negative marrying. I've read where others have said that it's negligible. Personally I've never really worried about it much and have yet to experience any real effect. As my cigars grow older and older, I expect I will eventually begin to.

I don't think there's any way to do away with it completely. Even in a well ventilated walk-in, you'll still get some oils flying around in the air. The best we can do is minimize it to the greatest extent by segregating wrapper styles. Maduro with maduro, natural with natural, strong with strong and so on. Leaving the cello on will also help, but not much. Keeping them in original boxes works even better.