Yes.
It would be used with
DAS exactly the same way as when not using DAS.
THe person the DAS was issued to must ride - I realize you said the one in your family with a DAS would be, but just clarifying for other readers - I know one of the past misuses of the GAC (Guest Assistance Card) was using it for attractions the person GAC was issued to was not riding.
Anyway. here is a link to a recent thread with more details.
http://www.disboards.com/showthread.php?t=3260329