The same inputs are valid, yes.
As you point out, towing four-down imposes (virtually) zero "tongue weight" on the hitch. So, the factors to consider are GWVR, GCWR and hitch rating. In some instances, you may want or need to know the manufacturer's maximum towed vehicle weight rating as well.
Oh, and not to forget a very important factor, you should weigh the motorhome (preferably at each "corner") and ensure that the motorhome is not over its front and rear GAWR values, and that the tires are properly inflated to match the actual axle loads.
If you tow a trailer or dolly (and do not use a "Trailer Toad"), then the "tongue weight" must be factored into the calculations, such that it a) not exceed the rating for the hitch, and b) not exceed the GAWR for the rear axle.
2008 Holiday Rambler Admiral 30PDD (Ford F53 chassis)
2009 Honda Fit Sport