No, because they are not outstanding soldiers whereas all missionaries (except the Jesuit specialist) are equally efficient. Also, soldiers are just soldiers; you have lots of them. But missionaries do a lot for your civilization because they appease the Indians. At the same time, a missionary is a labour unit or figthing unit permanently removed from your civ, which means that the temptation to use your least valuable colonists as missionaries is very great.
Mind you, I think it would be an interesting change to the game if one couldn't turn criminals or indentured servants into soldiers without having first trained them in a school. Train them to become ordinary colonists, as in the original game. In this game, you can train them to become statesmen at one go, given enough money, which doesn't feel entirely right to me.