Buildtools.jar and craftbukkit are a different server type from FTB / Forge type servers.
FTB / Forge are modded servers (suports mods)
Craftbukkit / Spigot is a reworked vanilla server that suports plugins.
A mod changes parts of the server to do old thing sin new ways or adds functionality by adding and changing the server.jar.
A plugin do not change the server jar it self, but adds functionality throug a plugin API
So if you want to use DW20 and mods, wich is a forge type server with mods, you need to follow this method: Install FTB Infinity 1.7 server for noobs (infinity 1.7 is another modpack, but the install method is the same for DW 20).