Elite Grenadiers function essentially the same as standard Grenadier. However, they possess much tougher armor which makes them hard to take down. Moreover, they were thick helmets which allows them to survive one shot from a Longshot Sniper Rifle.
These Grenadiers also get an upgrade to their weapons; carrying an Overkill Shotgun which makes them lethal at close range. Moreover, they supplement their Bolo Grenades with Flashbangs. While these grenades are nonlethal, when combined with their stun affect and the overkill, the Elite Grenadiers are a force to be reckoned with.
As such, one must dispatch them from afar as quickly as possible before they get too close, or use JACK to either stun or attack them.