Absolutely.  Most greyhounds are not reactive they are either scared of other dogs or scared of being on a lead around other dogs.   If your dog is scared of other dogs – being around lots of different breeds in a controlled environment helps:   Your dog will start to understand how nice other dogs are and calm down.   This then shows the owner that he is not reactive – if he behaves in a class full of dogs, it is more than likely he is just scared and not used to other dogs – rather than being reactive.  This thought changes the owners mind set – they stop being SO nervous when other dogs approach – and because they are less nervous – the dog is less reactive.   When the owner reacts – the dog reacts.  Dog training can often break that process.   There is a huge difference between a reactive dog and a dog who reacts because he has no idea what the hairy, short legged thing approaching is – so he panics.