I've never rehydrated dry yeast, and never had any problems with fermentation.
If you're making a low strength cider, the juice is basically just water, with a little bit of sugar in it. So the yeast should rehydrate similarly to an all-water rehydration. The time that I would worry about rehydrating yeast was if I were making a very high sugar cider, like 1.100+, because the osmotic pressure would stress out the yeast.
But, whenever I make a beer that big I make a large starter, so that's never been an issue. I've never tried to make a cider that big.