I dunno, but snubbing is dissipative and will cost some efficiency
(arguably the energy might just be dissipated elsewhere and more
destructively, or with worse EMI emissions).
Snubbers don't necessarily decrease overall efficiency though; sometimes they improve it. But that depends on the type of snubber used and how aggressive the snubbing is.
Unless they gave specifications for the snubber, I don't see what more they could be expecting as an answer.