Isn't this an answer you can find in the manual? I mean if its not against the rules of Tibia its implied its legal and there's no refference in the rules in Tibia's website about this. There are certain features that are not available in tournament game worlds such as:
Stamina
Daily Reward System
Achievements
Guild System
Loyalty Skill Bonus
Highscores and Kill Statistics
PvE Arena Fights
Boost Events (e.g. Double XP/Skill, Rapid Respawn)
Offline Training
However, none of them have anything to do with the party gameplay. However, I would say its not that convenient since you're individually competing with people to reach the most amount of experience you can, if you party hunt with them, eventually whoever solely makes more exp will be on top, and you would have to chose between hunting only with them or hunting yourself since its time limited. But overall, answering your question, no, there's nothing wrong or illegal about doing this.