According to the gentleman who tipped me off to this cache of wood, it's highly unlikely to be pressure treated lumber. It's just plain wood from the shop.
I have also been thinking about mixing the shavings into soil, or perhaps into the compost first, and then leaving them to break down. They are a mix of smallish shavings and sawdust so my concern would be that if it's not well spread out, it would clump and then go mouldy.
In any event, the amount that's available is enormous. I have no idea where they send them to for disposal, but it seems like a tremendous resource for us to repurpose.