Yes, you can cash in the 20% coupon on online orders, until April 2nd. You can also get free shipping by having the order shipped to your nearest REI store, and then going to pick it up from there. Perhaps the cost to drive there would be less than the cost of shipping to your home.
I have been a member since 1975. I cashed in my 20% coupon on a new Yakima HookUp bike rack, and saved $ 71 off the purchase. My nearest REI store is 8 miles from my home, and the Redmond and downtown flagship stores are about 25 miles away. My pet peeve with the actual REI stores is how often they are out of stock of what I am looking for. In view of the 10% dividend especially, they are reasonably price competitive with many of my local LBS.