Sorry, but there is no way they are in any way hydrophobic. Just the opposite. Both hold a TON of water, and they wick very very well.
Here is a test I did a few months ago. This is a 2" diameter Plastic plumbing pipe filled with perlite. The bottom of the pipe is sitting on a dacron fabric that is sitting on a chamber with water in it. The water has to wick up aprox 10" to get to the top. The second pic shows what happens when you rest a cardboard tube on the perlite at the top. Within less than 1/2 hour, the tube was soaking up water that wicked up from the bottom.
As far as how much water they hold, I did some experiments on that too. Take some dry perlite, and weight it, then add water until its soaked, then drain off as much water as you possibly can. You will find perlite holds almost three times its weight in water.
Perlite = 6.2 grams dry.and 17,7 g wet = roughly 285% water by weight.
Vermiculite is similar, but I have not actually tested any myself.