If you PvP with your Charm Animal skill placed in your skill bar, yes, your pet will fight with you.
However, pets are generally considered by most PvP Rangers to be rather worthless (they die very quickly, unless Beast Mastery is REALLY pumped up), and you are better off saving your Attribute Points and those valuable Skill Bar slots, for more effective skills in PvP.
If you would like to try it, though, we'd love to hear about your experiences. Tips from a true beastmaster that can make a pet effective in PvP would be quite interesting to many a ranger out there.
