See some people are putting sumo springs on axles of their 5th wheels. wondering could that make a difference in handling. weren't they designed to help keep truck from squatting when loaded.
Only reason I could see to put them on a FW suspension, is if you are over loading it, past the GVWR. Yes, they are better served to level the TV. For improved handling of FW, adding shocks would make more sense, if not already installed.
In most cases if you over load the FW suspension, you will likely be over the OEM tire rating also.