Good idea, done it myself on the allotments, don't forget to wet it well before covering with soil. Also any compost will also help to conserve moisture together with a helping of blood, fish and bonemeal.

This is recommended in any year.

Around here, we would compost it and mix it in, and also shred some and put them on top of the soil once the seedlings were up. Our experience is that the drainage-stopping layer, and fermenting mass underground does more damage than good. That is partly because of our ferocious soil temps, though.

I always used to do it in the days when I grew more veg, drought or not. I did it with sweet peas too. Always had good crops