The First Order's Rocket Trooper is the evolution of the Galactic Empire's own Imperial Rocket Trooper. They thus bring into battle with them a Rocket Launcher. Their jetpack also allows for some flight with thrusters that propel it upwards as well as it forwards. The First Order's Rocket Troopers are equipped with automatic firing SE-44C blaster pistols with the Cell Mod.
Like the Imperial Rocket Trooper, all First Order Rocket Troopers have an orange pauldron, which canonically indicates that they hold the rank of Commander. This could be a goof.
The orange pauldron was not actually added until the launch of the game; despite likely being canonically inaccurate, this was likely done to make Rocket Troopers easier to spot and identify on the field in-game, and/or perhaps be consistent with the Imperial Rocket Trooper's rank.