Youll be fine using degreaser and water. Actually I believe using a pressure washer at a little distance is better than a garden hose because it uses less water. Things will get wet either way but having done both at work many times a week using a pressure washer wont get things soaked because often times newer cars plastic covers and such tend to bead up water.
I would resist the temptation to do this. The only potential positive result is a slightly cleaner engine bay. There are many potential negative results. Instead, wipe it down as much as you can with a rag, blow out dirt if you have to with pressurized air, even use a toothbrush or Q-tip if you must get it super clean in some of the crevices. Take the engine cover off and clean that with mild detergent and water, and put it back on when it's dry.