I would never waste good vodka to rehydrate something that was supposed to taste like beer. I don't think i could consdier something that had been dried up into dust as beer.

However, beer does offer the possibility of preserving a supply of precious fluid that is free from nasty growths that may harm you. Nothing that can grow in beer will kill you. At least that's is written in some of the homebrewing books I've read.

I would boil any liquid I intended to make into a beer, because bacteria in most cases will not make you beer taste better.