<p>Am I allowed to redistribute only parts of the DirectX package? (e.g. only the DirectDraw DLLs, without Show/3D/etc.)</p>

No. From the DirectX SDK Redist EULA:
DirectX Software Development Kit Redistributable Code
Redistributable Code is identified as
  all of the files in the following 
  "Redist" directory on the DirectX SDK
  CD/Download:
redist/
The following files in the above
  directory must be included in any
  distribution of  the DirectX Runtime.
DSetup32.dll 
  DSetup.dll 
  DXSetup.exe
  DXupdate.cab
  dxdllreg_x86.cab