Yes. All addiction is unhealthy; however, spending a lot of time playing video games is not neccesarily bad unless it is leading to predictably negative consequences in your life.. A former patient of mine who spent a lot of time on games, got a job working for a games development company getting the kinks out. If there are negative consequences, counseling may be appropriate.
Not good preparation. In genera, l military men and women tend to be "doers". When there are crises, they tend to the ones who immediately set forth to find solutions. They are not the folks that just stand to the side. In general, video game addictions put people on the sidelines and prevents them from fully engaging in life. A videogame addiction is not an impressive job qualification for the military.