(The following has been tested in a singleplayer world and server with plugins, both had the same outcome. Also note that I have checked the files of Dunsparce in the new 1.9.5 Version and nothing came up there either.)

I'm unsure if this is suposed to be as it is, but Dunsparce does not evolve into Dudunsparce (two nor three-segment form).
The following picture shows the Dunsparce file from the new 1.9.5 Pixelmon Version of the evolution string:


In the Dudunsparce file it does show the 'preEvolutions' noted as 'Dunsparce' as shown in the pixture below:


I'm unsure what the fix for this would be due to the way Dunsparce can evolve into two and three-segment Dudunsparce with a specific chance, though I hope this can get fixed :D

While all the pokemon are in the game now, not all of them have a model, and the ones with no model just use their sprite and are only available through cheats. Dudunsparce is one of the pokes with no model, and as such Dunsparce is not set up to evolve yet. It would mean a 3d Dunsparce evolves into a 2d Sprite of Dudunaparce.

Oh that makes sense then, sorry for bothering you in that case XD
Thanks for the quick answer!