Yes it can damage a player. Also, a little trivia from the wiki, when it does kill a player, no kill icon shows up.
Regardless, it does such a small amount of damage that it is not worth getting over an HE grenade. HE's a lot more potent and can damage enemies in a bigger radius, while the decoy's radius is slightly smaller and less potent.
One very critical thing to mention. The "fuse" times for the decoy is substantially longer than an HE grenade. If you want to really "damage" someone with a decoy, you're going to have to do so sneakily (remember, decoys also present a "enemy" indicator on the map), like in a corner or so. Basically, it's going to need super timing, and even then, the damage is nearly negligible (unless the enemy(ies) are at < 10ish hp