From our visit in Nov/ Dec 2016, none of the main casinos in the city of Las Vegas allow over night RV parking in their lots. Most of their parking is in garages anyway where an RV will not fit.
Some of the casinos have RV ‘campgrounds’ even some as far out as Boulder Highway.
I don’t even remember RVs in the Walmart lots, nor any RVs in the Pilot truck parking area.
The choice of where to stay IMHO depends on where the wedding will take place. Las Vegas isn’t a hard town to get from place to place.
Do note that much of the ‘town’ of Las Vegas is actually unincorporated Clarke County. So what might not be allowed in the city of Las Vegas might be allowed in the county, like the two Walmart’s near either end of the airport.
(We are Thousand Trails members and stayed at their CG for the max allowed stay before moving to the military campground at Nellis AFB. Had to stay almost 6 weeks due to a medical issue. If you are a TT member or military/ retired both would be fine. )