Here's my take on this. On our previous 5er it had that make believe 1 1/4 hitch. Installed a Swagman 2 Bike rack using a 1 1/4 to 2 adapter. Mounted the bikes and checked for movement. WOW did they move around in all directions. So our first trip I added a ratchet strap from the bike rack to the RV ladder and put sufficient pressure to cut down on the bike movement.
Since we've changed RVs to one with a real 2" receiver and now the bikes are solid without added the extra strap.
So my suggestions, get a real hitch installed or take your chances.