My understanding is that as long as what you're providing for redistribution is a displacement map, and not the mesh with the map baked into it, you're fine: to use your map, someone still needs to obtain the original mesh from the owner of it, which is what mesh makers are trying to protect.

Look at it this way: you're making their property MORE valuable by adding content like displacement maps for it. If you're providing their mesh (even in modified manner) you're undermining the value of it, which is what upsets the owners.