So if you were to buy a ticket from Wimbledon on your Oyster card you would receive a National
Rail discount if due as well?

Would this apply to travelcards (say Zone 1-3) as well as season tickets (Wimbledon to Waterloo)
and do they have to be any minimum legth (weekly/monthly etc)

Are these National Rail % discounts listed anywhere?

You can't buy Wimbledon to Waterloo season tickets on Oyster only zonal ones.

The £1,000 annual Wimbledon to Z123 comes with a 5% discount if you renew
at Wimbledon. Here you can see how much you can get off the price:

http://www.trainsfares.co.uk/season/...p?sitecode=SWT

It only tells you the discount right before entering payment details - not when it
initially lists the ticket prices.