The hogs will probably use all sorts of things in their nests, if they don’t have much choice, but wood shavings do not sound ideal. i.e. they would not be waterproof like leaves could be if they are layered – I would think they would absorb the moisure and stay wet. So personally I would give the woodshavings a miss and rely more on leaves. Also, hay, is ok – up to a point. But longer grasses are helpful for weaving the nest all together and making a good sturdy structure.
Re. the feeding. I know BHPS sell Spikes and so probably think it is ok in terms of brands of hedgehog food. (Although I don’t believe selling something is necessarily an endoresement of it.) But that is not the same as recommending it, over cat or dog food, which, from their statement on their website, they appear to think is also as suitable.
Good luck with the cleaning. Hopefully there won’t be a hog in residence. All you can do is be as careful as you can.