I am going to guess - and it's only a guess, but like most other things with ADA compliance it would make sense.
1) ECV's - in order to be considered an ECV (and not a scotter, moped, etc) must meet certain requirements - minimum turning radius, minimum slope it can go up, minimum weight handling, etc.
2) In order to be ADA complaint, the queue must meet certain minimum requirments that accomidate the requirments for the ECV's.
That's not to say that the queue may be at the very edge of being compliant, but if it is ADA compliant, it should be able to handle a compliant ECV