As far as treason goes, giving aid and comfort to the emenies of the United States is treason, no matter who does it, military or civilian. As far as being in violation of the UCMJ, being reserve or active matters alot. Reservists not on active duty, nor performing inactive duty training, are not subject to the UCMJ! They retain their full freedom of speech, assembly and so forth, save that they cannot demonstrate or make political statements and so forth while in uniform or in a duty status. An inactive reservist,which is all he ever was once he left active duty, is not subject to the UCMJ, unless in receipt of activation orders and failure to go. In '72 he switched from inactive reserve to "standby reserve".
Technically even retired military (regular or reservist) are "in reserve", even if, like myself, they are not receiving retired pay. Only those who are discharged, and in the case of officers resign their commission, are not longer "in reserve". I suspect that for some reason Kerry did not resign his commision until '78, since his obligated military service time expired in '72. Since he was not an active reservist at that time, he was transferred to the standby reserve.
He became involved with protest in 70 or 71?