For a creature to show up, you need a custom hak which contains the model (.mdl) and any textures (.tga, .dss) it references.
The simplest way is probably to add the D20 hak to your module. Alternatively, you can open the model with a text editor (after decompiliation, if necessary) to discover the textures, which are named in the Bitmap statements.
You may also need a custom appearance.2da file in a top hak, adding the lines for your custom creatures to the latest Bioware 1.69 version (many older haks are missing 2da lines).
If you're using creatures from
http://neverwinterva...odern-creatures
I'd be surprised if you need CEP, as it isn't stated as a prerequisite.
If it turns out you really are missing something from CEP, you can export it from the CEP haks using NWNExplorer.