I do not own that particular model, but I've read on this forum that some have added mounts for various things to the rear bumper (spare tire, bike rack, grill mount, etc). Some have had to reinforce the rear bumper and/or its mounting brackets to do so. An issue may be that the existing rear bumper support brackets would not be strong enough to support any additional weight for accessory mounting bracket(s). While the bikes may not be heavy, they might cause their mount(s) to wobble a bit back and forth as you travel over rough roads or bumps. This wobble could transfer to the TT bumper mounts, and eventually cause them to weaken, crack, or break away.
A close examination of the rear bumper mounts/brackets would be the first thing I'd examine, and then make a determination if they need to be strengthened or not. Best to error to the side of providing them with some sort of reinforcement if they look questionable.
2015 Jayco Jay Featherlight SLX16XRB (TT)
2007 Ford F150 Tow Vehicle (TV)