As stated, you need park admission to ride the monorail since its only other stop is inside Disneyland at Tomorrowland.
Unlike Disney World, Disneyland Resorts two parks, 3 resorts and Downtown Disney are all next to each other in easy walking distance. No need for buses, boats etc.
The Grand Californian borders California Adventure and Downtown Disney and has its own entrance into CA. Disneyland Hotel is closest to the Monorail but GC or Paradise Pier hotels are also easy walk. Again, everything, parks, resorts, downtown Disney are all very easy to walk between.
Parkhopping is as easy as a couple minute walk between the two park gates.