Is a night VFR rating a prerequisite for an EASA CPL?
According to FCL.610 (IR - Pre-requisites) you need to have a PPL or CPL and a night rating to apply for the IR.
If you do not have the IR, the night flying qualification (NFQ) is no requirement to start training for the CPL. According to the AMC appendix 3 of the Notice of proposed Amendment (NPA) No. 2008-17B night flying is part of a training course for the CPL.And FCL.315 states, that the applicant for a CPL shall complete a trining according to the appendix 3, cited above.

SO: If you have the IR, you should also have the NFQ but you do not need the NFQ to start training for the CPL.
However, you only need 5 hrs night flying to get the NFQ and there is no examination, i.e. the FI rates your skill.