Every time I've stayed in a handicapped accessible room, the tubs had bars & hand held shower sprayer. I bring my own shower chair because the resort may not have one for you or it may not be the type you need. I have a transfer bench type that comes apart & fits in a large suitcase. I feel like that set up is much safer than a roll-in shower. You can just swing your legs over & you're on dry floor. I've never noticed grab bars in a regular room.
There are various types of "accessible" rooms at WDW resorts. Some have roll-in showers but several have tubs which will have grab bars. You'll want to look at the descriptions. I don't believe the "regular" (non-accessible) rooms have bars in the tubs.