It's possible at this point that they repositioned so that all DME buses have lifts, but I can tell you that it was not the case for our last trip in April 2016, at least not for OKW.
We have used the DME lift buses since DME first started running, so are very aware of what they look like.
As we waited at the airport for our bus to OKW, I saw buses in the pick up area without lifts.
We were quite early to the DME pick up point when leaving leaving OKW; we tried to get on the earlier bus going back to the airport. It was not accessible. The next bus was drop off only, but also had no lift.
The driver for our bus said the lift was not working and he would call us another lift bus. He said it should still be in time, but he did not know where the bus would be coming from because the bus that was nearest might not have a lift.
The Bell Captain ended up calling us an accessible taxi (which OKW gave us a voucher to pay the driver with). He said we could take whichever came first, but not to count on the next bus being accessible or an accessible bus getting there in time.
We ended up taking the accessible taxi, so I have no idea what would have happened with the bus.
I'll be interested in checking it out when we go in October