My understanding, which is admittedly rudimentary, is that Disney has no legal way from stopping Uber and Lyft from dropping guests off on property. Whether the company can prevent pick-ups, the same way the airport has for years outlawed pickups, is another story, and I'm not entirely sure of the answer. The legal situation regarding Disney property is so convoluted and strange that it would take someone with a better legal mind than I to untangle it.The roadways are Reedy Creek's, but the resorts are private property, and probably the theme park lots as well. IMHO Disney would be within their rights to exclude Uber & Lyft from the resorts & park lots.
DS is a gray area to me. The surface lots may be Disney property. I think the new garages were built by Reedy Creek for tax advantages, but I don't know who technically has control of them.
All that said, I'd be surprised if Disney ever tries to fully outlaw Uber and Lyft from property. I know it's the prevailing belief at this point, but I don't foresee it. Time will tell.