you must be new to RV forums.
this is discussed all the time and ultralite trailers, like hybrids have extremely weak bumpers. they are more decorative than functional.
only because the spare tire is right up against the trailer, can the bumper support it without the welds breaking.
a bike rack will hold the bikes out and away from the trailer. the physics of this will eventually break the weak welds, from the bouncing of the bikes, since your trailer has no shocks.
only those who have a 2" receiver welded and braced to the frame and bumper, can get away with bikes on the back.
but, doing this mod, will void the frame warranty, according to the manufacturers.
if you'd like to do some research, just type in "bike rack" on any RV forum.
you'll find hundreds of posts and pics of mods.