
You're quite right Fiona, the Kennel Club will give permission.
In reality I doubt if many spayed bitches are 'notified' (who can tell?) and castrated dogs are very unlikely to be placed, so they aren't shown much.
Edit: I suppose a vet would vasectomise a dog, and yes, it could be shown, because the breed standards only say that "male dogs should have two apparently normal testicles well descended into the scrotum" - nothing about whether they are fertile or not.