They can be briefly stopped, yes! Magic swords like Guren's will be able to do damage when they're more tangible, anything that creates light will be able to briefly stop them as well (because, after all, they're shadows) -- anything along those lines will work!

The problem is just that it's all temporary, since the shadow is going to be around so long as the character's around to generate a shadow. So he'll be able to help in the moment just fine, there's just no really good permanent solution, if that makes sense!