First, let me let you in on a little secret re: lodging near
Disneyland. Everything is "15 minutes or less!" Places advertised as "right across the street!" can still be a 20 minute walk, because they are across the street at the far corner of the park, as far away from a pedestrian entrance as possible. It takes most people about 10-15 minutes to get to the pedestrian entrance from Katella and Harbor (technically, still "across the street!"). And the "blocks" in Anaheim aren't regular city blocks... they are much, much longer (ie, multiple hotel properties can make up one side of a "block").
Going off my state's rules (assuming that other states are similar), to receive a disabled handicap placard for parking, you can't easily walk more than 200 feet. I'm willing to bet that there's going to be a heck of a lot more walking from the car to the pick-up point for the tram, and then from the tram drop-off, through security, and over to the
ECV rental area. I mean, yes, there are benches the whole way, but I'd assume that would still be pretty darn taxing for a person with mobility issues.
For the reasons above, I'd rent locally (Deckerts Medical Supply and Apple Scooters both get high ratings here on the boards), and walk to/from the parks, with those who need it riding their scooters. Especially at the end of the day in the parks, it's a long walk back to the tram, then to the car from the tram.