Yes. Aero also concerns the inside of the car...
That internal skin 'smoothes the edges' of the internal parts of the car, covers the big cables and the pipes, reduces the seams, closes the gaps, prevents that the air dissipates under the main bodywork, helps it keep enough pressure and energy and guides it where it should go. It can also have a heat shielding function.
So it's is an important part and its absence must be hurting the car's aero and maybe cooling too (hence the big rads and intercoolers?)
RB11
https://pbs.twimg.com/media/CT2e6YKWsAI3Rzr.jpg:large
RB10
http://img2.auto-motor-und-sport.de/Red ... 769719.jpg
An FI with and without it