Characters with the Martial Artist edge are not considered unarmed, which means that other armed characters do not get a +2 on their Fighting roll as per the Unarmed Defender rule (SWD, p76).
However, are they considered armed so that they do get that +2 bonus against other unarmed characters? Neither the Martial Artist nor the Improved Martial Artist (SWD, p36) make any mention about this.