That's a clever idea, and I can see it gong either way.
It's true that a vacuum will desiccate what's in it. But when it comes to vacuum packing, the volume of the "vacuum" is tiny (since the plastic forms to the shape of the object inside), so would be expected to effectively instantly saturate. and ceased drawing out water. I seriously doubt the brief time period exposed to suction will cause any measurable dehydration.
The obvious pro to having it sealed is that once it's sealed in there, your water loss will decrease to near insignificance. My main concern would however be that there's no oxygen getting in. Yes, plants photosynthesize to produce sugar, but their cells still "breathe" with oxygen when they burn sugars for energy.
So you know, I really don't know what the net result would be.