It is supposed to account for both. It's ridiculous that people with disabilities are forced to wait LONGER than standby, and they should fix the situation - and hopefully will. The whole "it might all equal out in the end" idea is just ridiculous when you consider that the point of the DAS is to help people who can't manage regular lines. Plus, oftentimes the early morning SB times are LONGER than actual, so people with DAS are already likely waiting longer overall.
In the meantime, I have heard that if you are waiting longer than 10min in a FP+ line, you should go to the ride CM and tell them, and they will give you an anytime/anyride FP.
More time than not the SB time thats marked is way off and it takes WAY longer so the people with the DAS are getting in way before even with the ten min wait in the FP line. It works both ways.