The answer is yes, of course you can camp in those walk-in sites. They are just that: available to anyone walking in and claiming one. If they are full (probably never happens, especially this summer with the parking restrictions), there are more below the main backpacker parking lot -- the Ravine camping area.
I'm thinking if we hike that far down we may just camp at Lone Pine Lake. That is if we choose not to drive home that night. We've never camped or even walked over there. I have stayed at the Portal a couple of times. Plus we'd save the campsite fees.
Is it a nice place to camp? How about Outpost?
