Re: Hive material
Wood crates and pallets that come into the US from other countries must be treated to prevent pests that might be in the wood from entering the US. The two treatment options are either heat (essentially kiln drying) or fumigation.
The wood must be marked with the treatment method, so you should look for labels on your wood to determine which method was chosen. (I see quite a bit of wood stamped "HT" for heat treated.)
If the wood was heat treated, it should be stable enough for building woodenware. If it was fumigated, perhaps you should explore more exactly what was used and what kind of persistence it might have.
USDA Zone 7a - elevation 1400 ft