This park surrounds the Scadding Court Community Centre, which hosts great events for the community like cheap lunches and local meetings. There's an indoor pool and an outdoor one -- the outdoor one is free and during the summer nights, some people are known to climb the fence and go for a late-night swim. In the winter when the pool is closed, beware of the "park" area -- it gets SO icy! Stick to the paths and you'll be fine.
The park itself is definitely a popular skate spot, I know of many people who are here on a regular basis to skate all night and take a break at McDonald's across the street.
But as for a night-time walk...I lived in the area for a couple years and I still don't feel safe around Denison and in the park. Maybe because I know a handful of people who've been mugged or attacked in the area, but it's just not a great place to be at nighttime. Except for in the pool during the summer :)