This is a very simple question. Take some personal responsibility and examine your situation.
Is your rear bumper strong enough? As many have indicated, the thin bumpers tend to fail when subjected to extra stresses. Reinforce it if needed.
Does your bike rack hold the bikes from moving? Moving around and bouncing are multipliers of the stress and loading on the bumper, more so than the spare tire since the tire is generally closer in and does not move around.
Does your trailer bounce much going down the road? Some trailers have a tendency to bounce, this puts more stress and load on rear bumper when you have bikes hanging back there.
If your bumper is strong enough and you secure your bikes well, then just do it.
You don't need permission from this forum to do so. If you neglect to properly mount and secure your bike rack, you won't get much sympathy from this crowd... if your bumper tears off the frame and ruins your $1500 bikes, you won't get much sympathy from this crowd..
To be honest, not many trailers need extra weight on the rear, most need more on the tongue. My Dad has a Komfort that has the axles towards the back and he was able to put a platform on the back for his generator and gas cans. If your axles are not towards the back, please be careful of adding the weight back there. It could upset things and cause sway.
Best of luck! It can be done, you just have to pay attention.