Yes you can use your colleague discount on George.com. Here's how:
On the payment page select pay with an eVoucher
Add the code ASDA
Enter your Wal-Mart number and Discount Card number & submit your details. (You'll be able to see that your discount has been added in the basket Summary on the right hand side of the page)
Some policy stuff
The Colleague Discount Card is a discretionary benefit and not a contractual right. Full details of the Colleague Discount Card scheme's rules are contained in the Colleague Discount Card policy which is available on the WIRE. It's your responsibility to familiarise yourself with the policy.
Grocery Home Shopping is not included in this benefit, and George.com will not be included in Special Discount Day activity.