Aircraft data available from these sources: Internal Database
Aircraft data used by GSX: Internal Database
This means it's not possible you'll ever see either of the two vehicles ( Tanker or Hydrant ) that have a guy because, as I've said, the refuel point we configured for the PMDG 737-800/900u is set lower than the lowest ( 3.40 meters ) any of these two vehicles can reach, which means the smaller truck with no guy will appear.
I checked it now, and even with the airplane very light, with only 5% of Fuel, the refueling point height was set at 2.96 meters, which is lower than 3.40 and sure enough, I always get the smaller Fuel vehicle, the Isuzu 7296, which has no platform and no guy.
Be sure you restart Couatl before applying a new config. Switching airplane will do that automatically.