I see people spray a hose on their engine inside the hood to clean it with the hood? Is that a dumb thing to do or recommended??

It's sloppy, yes.   If car has good, tight,  o ring sealed connections; no amount of water will affect it. Possibly, wet plugs can Temporarily short.  A wipe with a dry cloth or waiting 10 minutes will "fix" it.

   Note--12 volts CAN NOT be "shorted" out by ordinary tap  water. Maybe Salt water. Water Might affect brushes/slip rings/commutators Temporarily; but a few revolutions of alternator/Generator shaft will throw it clear.  Solid-State Regulators  and  rectifiers are Hermetically Sealed.   Car engineers aren't Stupid; they know a passenger car will go  thru a few puddles. 

   I have used gunk,  then a nozzle just to greasy parts of cars,   no problems. Indiscriminate use especially on an older vehicle might get water in the breather and inside the sump.

  Fuse box on my old Chevy is coated with thick layer of tar , from Factory, to  preclude any such malarkey. I undercoat all my  cars, too, just in case. Takes 4 cans of spray U/C..

    Many engine steam cleaners  are out of business, due to both  pandemic   and pollution laws tightening. Even do-it-yourself  car washes discourage using Gunk , say U must use their organic degreaser, only.

That is a reckless thing that can short electrics, especially the alternator.

A CLEAN ENGINE will last the LONGEST and operate the BEST for FUEL ECONOMY as it will DISSIPATE het more evenly! To remove the ROAD KILL from the RADIATOR along with DEAD GRASS and LEAVES and TWIGS will keep it running the COOLEST! AND FILTH on the NEIGNE holds HEAT IN! ALLCARS should be POWER WASHED under the hood every FEW MONTHS! MICE and RATS like to EAT the wiring harnesses and KEEPING IT CLEAN helps to DETER THEM! RUBBER hoses and BELTS will last LONGER and the AIR wil ACTUALLY be CLEANER as the engine will NOT hold in the HEAT is much and things stay COOLEST! MOST cars today have CRANK POSITION SENSORS that are ELECTRO MAGNETS and VULNERABLE to ENGINE HEAT! To keep an running it;s VERY BEST, YOU NEED to keep the ENGINE bay AS CLEAN s as SHOWROOM. IF there are PLUG WIRES they wil LAST LONGER as the CLEAN allows HEAT to DISSIPATE and PREVENT ROTTING of RUBBER inuslagtors and MORE! IF the crank SENSOR gets TOO HOT>> it will STOP WORKING and leave you STRANDED someplace with a DEAD ENGINE!  AND your radiator VANES will get full of BUGS and RoAD KILL and DEAD GRASS that INHIBITS proper engine COOLING! >>>YES I RECOMMEND IT! CLEAN is the NAME of the GAME! Using PENNZOIL On the INSIDE keeps everything's CLEAN on the INSIDE and GUNK ORANGE engine cleaner keeps it clean on the OUTSIDE to be MORE EFFICIENT and to GET RID of excess HEAT! GUNK ENGINE CLEANER is mostly DIESEL FUEL and DISSOLVES the baked in **** on the OUTSIDE and the BAX is WRONG HERE AGAIN! To CLEAN is NECESARY to remove BUGS and ROAD KILL form the RADIATOR and the AC condenser!  Do you like OVERHEATING??? the ENGINE BAY cannot HELP but to collect JUNK from the ROAD at HIGH SPEEDS! I have CARS out there with ALL ORIGINAL WIRES and BELTS and HOSES as they are CLEAN on the OUTSIDE and using the RIGHT COOLANT are CLEAN on the INSIDE as well! NONE are GM cars and MOST are EURO CARS and ASIAN ones and FORDS! 

It's a dumb thing. Pros will use a steam cleaner and they know exactly what to cover or blank off. There are a lot of electrics and electronics under there and they don't get on with water. Any dirt under there is going to be oily/greasy and straight water won't shift it anyway. 

Do you wash an electric fan?  No. The engine has harnesses, motors, sensors and connectors.  They do NOT like water or moisture.

You will mess up the connections on the harness.  Motors get dirty. Quit worrying about the motor and you'll be fine.

I have used my power washer under the hood of my cars and never had an issue.

HOWEVER - - I don't spray near any electrical connectors or the fuse box.

I've been hosing out engine compartments for almost 50 years without an issue. Just be careful where you spray.

Spraying with water is not a good idea.  It won't remove grease and oil.  It could short out anything electrical.  Steam cleaning by professionals is the best way to go.