Can an expansion tank described as for a water heater be used for a boiler system?
Can a expansion tank be used to protect a hot water heater? YES.
Dose it need to be thermally listed? Not really if on the cold water feed and a check valve in the input of the pressure tank. 
The thermal cycling water really won’t heat the expansion tank, as the water is not being used when the water heater continues to heat some hot water pushes back into the expansion tank the hot water in most cases only makes it back a few feet. The water heater tank is now hot and full. Slowly cooling, but the supply line rapidly cools. The water moved from the tans back to the water heater once the water heater tank cools the cycle starts over. I have installed several dozen small expansion tanks and have never used anything special. The closest my expansion tank has been is on the floor next to the water heater that did not have any problems many were 20’ away. So I just use a small bladder tank nothing fancy.