Hello.
You can equip one pet on 2 characters in arena 2v2. To do that here is an example:
Equip the pet you want on your hireling and do one match in the arena. Now equip the pet from hireling on your main and do a 1v1 arena match again. Now you have 2 characters on arena with the same pet on a 2v2 fight. Bug or not, that may be not intended 
This explains the many people who have the same pets on their characters in the hacker/cheater post
Also, this apply to every item not only to pet when I thought about it more. So you can have one good trophy that 2 characters could use or even the whole set of items.
This is intended and only works for the AI. To reduce data usage, only your char is uploaded when you PVP.
AHA!! I thought your doing a cheat Msiiek because I saw your Warrior and Rogue with same Items and Pet Thanks for realizing me that Im wrong 