All Wolves are hostile, but they can still be charmed.
The default animal companion for PvP characters is a level 20 Elder Wolf (a Wolf with the "elder" evolution). Whenever a PvP character equips Charm Animal, if they do not currently have any other animal charmed, they will receive an Elder Wolf.
Level 15 Elder Wolves will sometimes spawn near Thul The Bull and other groups of Stone Summit in Spearhead Peak for the rangers to charm. By flagging your heroes/henchmen off the radar to one of these group's spawn point, they can be killed/interrupted before the wolf can be charmed.
Other species of wolf can be found throughout Tyria: