Somimp_view.exe is an app you can find floating around the Sword of Moonlight community. It is a build of Assimp_view.exe with code beneficial to Sword of Moonlight users which has not yet been officially adopted by the Assimp project 'rolled' in.
It can display MDL files and many other model formats. To use Somimp, simply drag a file into its window and select the animation set you want to watch from the drop-down. You will have to push stop/play every time you switch animation sets. If one of SoM's MDL files will not play its animation, it is most likely a 'soft' animated model (like the Slime shown at the beginning of this document). Somimp and x2mdl can not handle this type of model yet. Keep in mind that non-MDL files will sometimes display ok in Somimp, but will not properly convert to MDL. Similarly, if your non-MDL file displays poorly in Somimp, it might still convert to an MDL properly. However, when Somimp is displaying an MDL, that is what the MDL will look like in an actual game.