Yes. If you are a doctor in a training programme, aesthetics work is other professional activity and belongs on your Form R, the same as locum shifts. Omitting it from a revalidation declaration is a probity issue, which is a far bigger career risk than any conversation the declaration triggers.
The anxiety behind this question is usually cultural rather than regulatory: trainees worry about being labelled uncommitted. But the regulatory position is simple. Your licence is one licence, revalidation covers your whole practice, and the Form R asks about all professional activity. Declare it, keep it compliant with your hours and contract, and let your NHS work speak for itself.
Our NHS-and-aesthetics guide covers the wider picture, including appraisal evidence and what happens if you eventually leave the NHS and need a designated body.