Military, including JROTC, CAP, Sea Cadets, & Young Marines: No, for everyone in the military- it is not authorized except for the funeral of a POW. It is not usually carried in a military color team, but it can be included on special occasions. The standard for the military is to carry the POW/MIA flag separate only for the funeral of a former POW as in the picture here, courtesy of www.arlingtoncemetery.net.
First responders and veterans groups: My advice is to not march a POW/MIA flag within the team formation since none of the service honor guards ever do. It can be appropriate to march it on its own (like a Personal Color, a general’s flag- see the above picture) without guards- however, color guards in this category follow a service D&C manual, which then dictates that you should follow the manuals that affect it. Many veteran groups who have a color (guard) team carry it as part of their standard compliment of the American flag, the state (or specific service) flag and then the POW/MIA flag. Depending on your location in the US, you will hear some very strong convictions (yelling matches) on whether it is OK to march it in a color team or not. Strong convictions do not replace written standards.