My dad always uses his
ECV for
HHN. We get Frequent Fear Passes and go a bunch of times, and it's definitely doable. Now, that being said, there are a few caveats.
If you are able to walk through the houses, definitely do so. The ECV will not be allowed inside. Standard wheelchairs are allowed, and you can transfer to one at each house, but a lot of times you'll have to bypass certain things (like the vertigo tunnels or the aforementioned claustrophobia walls). If you need the wheelchair, use it, but if you are able to walk, it enhances the experience. Dad uses a cane when not in the ECV, and it's never been a problem in the houses.
If you qualify for a Guest Assistance Card, get it. If not, get an Express Pass. The lines are usually crazy long, and the standing and waiting can be worse than the walking.
Even using the Express entrances, it can be a long way from the line entrance to the actual house, and you might exit in a totally different area. Sit down with a guide map and plan a route that minimizes walking.
Example: last year The Hallow loaded through the Barney theater, but exited by Men in Black, right by the entrance to Dead Exposure, which circled around and exited by its entrance. So after a few nights' experimentation, we hit on this order. Dad parked the ECV by the Dead Exposure exit and walked to The Hallow. He did that house and then Dead Exposure, and by that point desperately needed to sit down. The ECV was right there, making it easy. Likewise, all of the soundstage houses exit in basically the same location. So he parked the ECV at the exit, walked to the furthest SS house entrance, then did the three in order, then retrieved the ECV.
It definitely takes planning, but HHN with an ECV is entirely doable. Just remember to keep the speed turned down, and expect other people not to notice you exist. Dad was at a dead stop one time when some guy came running along at top speed looking back over his shoulder. The guy collided with the scooter and landed on his stomach in the basket! Crazy nights, but a lot of fun!