Wasp is right.
As a proof for your opponent, you can use the very first entry of the DE Q&A:
"Chapter Approved – Codex: Dark Eldar Q&A (v2.0)
Q. The Reavers get the result of 1 on their Combat Drugs roll and never fall back. The Succubus in the squad has her own drugs, and the result of ‘Crazed! Ignores fall back results...’ is not available to her. Now, if the squad loses combat, they will not fall back because of the squad’s drugs, but will the Succubus have to make a Morale check and possibly fall back
(thus leaving the squad)? This is only an issue because she is not an Independent Character.
A. Hmmm, this is a good question. Overall unless all of a unit is immune to falling back (for whatever reason) it is best to assume that the unit will fall back if they fail a morale test. Under no circumstances should a unit be broken up and it is unfair for models that do not have a fearless or similar ability to benefit from being in proximity to some that do. There are some exceptions to this, for example Warlocks who are joined to Wraithguard units but these exceptions
should be specifically stated."
This would make absolutely no sense if a combat drug dispenser of the succubus would affect the whole squad.
jwu