Depends.

They're texture replacers; so everything that can go wrong is you seeing texture A instead of B.
If you use no other texture mod, it doesn't matter in any way where they are. If your other replacers affect only textures not touched by the DLC, it doesn't matter, either. (I don't know of a simple way to check that, currently.)
If you use some replacer for some textures also affected by the DLC and want to see these instead of the DLC, the DLC should load before that other mod.
So essentially: They're very generic replacers which you might want to override in some areas at some time. As such, they're best placed rather early in your load order. Where exactly, matters only in relation to other texture replacers.