Pretty much any wood can be used for a turkey call. I know a guy who only uses cedar and he makes a great call. Cherry, walnut, maple, hackberry, osage, and hackberry are very popular woods. Spalted woods, crotch wood, and burls can be used.
the important things i look for when deciding what wood to buy is just like everyone else. Figure and unique. Unlike alot of other turnings, the wood has to be around 8% or less in Moisture content otherwise the pot when hollowed out will move. Once it moves then the pot is worhtless. When we build pot calls, we build it around a specific piece of glass, slate or aluminum. If the move twists or warps, then the plate won't sit correctly and through off the call.
I love the Walnut you have listed and if its dry and you post it for sale, depending on price, i would love first crack.
Jason