RocketSims are pyromaniacs; they will always use explosive weapons if they have them available. If they do not, they will still shoot bullets. Their scripting is barely different then that of higher difficulty simulants: Higher difficulty simulants (Normal+) always use the explosive function of their weapon. However, they always use their best weapon. If the weapon was a SuperDragon, they would fire off some grenade rounds before shooting bullets. The RocketSim, however, depletes the explosive rounds of a weapon, then switches to another explosive weapon. If there are no explosives, it shoots bullets.
If these Sims are in your game, stay away from closed areas! They WILL fill a small space with flames, regardless of their own life. You will find yourself in a fiery coffin with no way out. In open spaces, you can dodge the projectile, or at the very least, jump out of the explosion.
These sims are very useful in Capture the Case when defending. They will risk their own lives by shooting their explosives at any attackers. When attacking, however, making them get the case isn't wise; they may blow themselves up just as easily.