No idea about the downhill.
All the other trails were fine as they decided in their wisdom to build most of the bits that get muddy into rocky and dumpy throw you off the saddle trails, which is no fun bouncing all over the place.
I've ridden the DH trails in absolutely torrential rain and it was ok. I mean muddy and slidey - but generally ok! I do take things easy though and am rather cautious on DH trails
Just go with good tyres, be prepared to get VERY muddy and go for the odd slide off the trail