A prop is something your lo needs ALL the time to go to sleep, if you use something like the swing or car/pram for the occasional naps it is fine, infact a good idea as they get used to not always sleeping in the one place. It will also allow your dw to get out & about (if your lo sleeps in the pram) & have a bit of a social life, which will actually give her the strength the deal with crying, as she won't feel a prisoner to the nap routine.
With my #2 he ends up having at least one nap a day in the pram &/or car & used to have quite a few in the pouch until he got too big 7 he goes down like a dream, in his cot most of the time unless overtired