Based on squadron usage, the holes in the Red Baron 3D planeset were:
British: Armstrong Whitworth FK8, DH5, Sop. Dolphin, Vickers FB5, and minor player - FE8
French: Hanriot HD-1, Morane L, Morane P (RFC usage), Voisin LA3 and LP8, Caudron G4, AR-1,AR-2.
(Caudron R-11, though widely covered did not show up until mid-October 1918.)
German: LVG C.II, LVG C.V, DFW C.V, Albatros C.VII, Albatros C.X,Rumpler C.VII (C.IV with high altitude engine), Junkers J1/J4, Siemens Schuckert DIII.
The German observation units would use a variety of planes based on altitude needs of an assignment. So, you may have dFW or Albaros C.VII ,mixed with a Rumpler for the high altitude work.