The Weaponsmaster plays a role and is encountered during the Shield of Arravquest. If you are a member of the Black Arm Gang he will attack you. The Weaponsmaster will attack you if you attempt to take either of the two available Phoenix crossbows (both are needed to complete the quest). As a result, he must be killed in order to get them. He will also attack members of the Black Arm Gang if they try to talk to him. He is found upstairs in the southern alley of Varrock.
After an update, Phoenix Gang members can no longer attack the Weaponsmaster. In the past, if a member of the Phoenix Gang tried to take a crossbow, he will notify them that it belonged to Straven and prevent them from taking it. After an update a message will instead come up, saying, "I'm not going to attack a fellow gang member." This is ironic, as the thieves inside the Phoenix Gang's base itself can be attacked, though they may not necessarily be part of the Gang. However, members of both gangs, or even those not in either gang, can cast Telekinetic Grab once they arrive in the weapon store room to take these crossbows, but may be noticed if you have already spoken to him.