nope... a "Jake" or Jacobs engine brake works by actuating the exhaust valve just before TDC on the power stroke... this allows the engine to absorb as much energy as possible by compressing the air, then releasing it through the exhaust. this prevents the piston from regaining energy from the compressed air in the non firing cylinder. a compression brake can absorb upwards of 400HP. this is what the big boys use and gives you the staccatto rumble.
an exhaust brake works by building exhaust pressure that the engine must fight against. this gives "compression braking" comperable to a gas engine of equivelent size. (gas engines's intake throttle blades performs more or less the same function when closed). when actuated, these just kind of hiss.
check out
-Bret