We were there and rode it several times less than 3 weeks ago with DD in her wheelchair. We were also at WDW in late December/first week of January 2015 and rode several times.
We had Fastpasses, but also saw people who were using wheelchairs and did not have Fastpass.
With Fastpasses, we were sent directly into the accessible area. Guests with wheelchairs and
ECVs who did not have Fastpass were sent in the regular (Standby) line.
The Fastpass line is on the side of the attraction nearest the Rapunzel area (years ago, that was the exit). It is not accessible because it puts guests on the wrong side of the water compared to the wheelchair boarding area. The route of the Fastpass line doesn't come near the entrance to the accessible area.
The Standby queue runs across the whole front of the attraction. It makes several turns (how many depends on how busy it is and how they set up the chains). The last turn before joining the Fastpass queue is next to the entrance to the accessible boarding area.
We saw people with wheelchairs/ECVs waiting in the Standby queue until it reached that turn. At that point, they were pulled out of line and sent to the accessible boarding area.
I would call it a partially Mainstreamed line.
Prior to that, CMs were giving out wheelchair return cards for guests who needs to use the accessible area and didn't have Fastpass or
DAS.