If someone disembarks or boards on a Cessna the door and wing strut generally prevents someone walking into a live prop. like wise on Pipers the door again prevents someone walking into the prop.
The problem is with aircraft with sliding canopies such as the Bulldog, Grob115, Robin DR200, DR400, the poblem is boarding with the engine running, that you could slip on the wing and fall of the front of the wing, likewise upon disembarking an aircraft the danger is 'going the wrong way' and jumping of the leading edge into the propellor. I was warned of this when I started flying DR200s, as I was told this happened with fatal results at Sywell in the eventies and eighties.
During my career on several occasions I have seen people hand swinging aircraft, when there is no occupant in the aircaft, utter maddness!
Historically, the RAF did live changeover of air cadets on on the DHC Chipmunks as the had explosive cartriges and their were only six, but the air cadet was always ecort. It would be interesting to know what happens on the RAF grob? In the instructing world instructors have in the past asked student pilots to start the engine and then board.
As most modern aircraft have electric starters, there is no need for anyone to board or disembark with a live engine. On aircraft where handswing takes, the person who is handswinging and the occupant should be sufficiently qualified, trained and pre=briefed not to walk into the prop,