You can rollerblade in Stanley Park. The only place that you can actually rollerblade is on the bicycle path on the seawall. Rollerbladers, along with skateboarders, are treated the same as bicyclists so need to use the bicycle path on the seawall. This path is one way, counter-clockwise, around the park.
Most of the bicycle rental shops also rent rollerblades...check out our: Bicycle Rentals page for more info.