My Blissey hasn't even been leveled up from 20. I tend to put weaker stuff in gyms. Right now there's a Granbull, a Breloom, my shiny Aggron, and my newly-hatched Lileep, I've made half the park (4 gyms) blue, while the other half is from the red side who don't yet have 8 hours anyway.
While I do consider it, I do not know if Niantic really cares if a freeloader reports this. I'd much rather wait until tomorrow and write a rant on the group, asking for video evidence that I am not there when I take a gym.
I was trying to get some TMs and gold raz + a good starter's 2nd evolution, and also to allow the others to get their rewards too, which I thought was a win/win, since we both were in the lower 30 levels.