Sometimes yes...sometimes no. We stayed at ASMu last week. Dh and I tried to figure out when the All Star resorts get their own buses and when they don't, but we came away totally perplexed. It felt as if we shared buses during the busiest of times.
We just returned from ASMo. MK is the only place where you have your own bus. There is even a seperate bus stop there now too. For the rest of the parks we had to share.