Some do. There is no hard & fast rule saying that you need to vent out the roof. It's just that heat rises and most vents do not have a fan. Close to the ceiling would work and you may want to add a small fan to the setup. If you will be in areas with temps above 90F then you may want to add a fan to your vent anyway. RV refrigerators do not like to get hot.
We do not have RV deathtrap fridges.We think they are accidents waiting to happen. We have 110vAC under counter refrigerators (2) and a house type 12 cf upright freezer. We use vents in the sidewall and no fans.
The fan forced vent for the range is on the left. The vent for the two refrigerators is on the right under the marker light. The freezer vent is identical to the refrigerator vent. (click on image to see whole picture)
View from inside (we have a fiberglass screen over the vent to keep bugs out.
The louvered section of the original RV refrigerator access panel on the Class C was about the size of the louvers on this vent. Hold one vent at the window sill and put a 3" floor/sidewall vent at the top of the window to allow convection air flow to pull the heat away from the fridge and out of the bus. I got the vents shown here from Home Depot in the heat/Air duct area. You will need to be able to open the larger vent to access the rear of your deathtrap.