In general,
DAS is not used for the parties because waits for lines are short and they are using only one line.
With only one line in use, there is no way to bypass the line to get past the other people and no Standby Wait time to base a DAS Return Time on.
Whether or not you can use it for individual attractions is going to depend on the attraction and what they have available. I have heard of them using DAS during parties for attractions like Big Thunder Mountain Railroad or the 7 Dwarfs Mine Car ride.
DAS is not available for the special character meet and greets. They are in areas that don't have a place to bypass the line. For some, you might be able to have part of your group wait in line while the person with a disability and another member wait outside of the line.
The meet and greets that have permanent locations (Fairytale Princess Hall, Mickey in Town Hall, Tinkerbell, Side Show in the circus area) usually have short lines during the party. I would not count on usin DAS in those locations, but it might be possible.
I would consider a wheelchair or stroller as wheelchair.