Not sure if it has been a issue with Universal running out of ECV’s in past. You might give guest services 1-407-224-4233 a call and see if this has been an issue in the past or not. I’am not sure if you can reserve a EVC or not. Worth it to ask for sure.
It appears that HHN will be busy this year if the sellout of some of the Resorts is any indication. There also seems to be a big buzz on social media about HHN this year. Folks have been closed off because of Covid and want to get out.
Some options that might help your experience of HHN with your dad.
1. Weekends are busier. Look at the calendar and pick a day during the week like Wednesday or Thursday.
2. Not sure if this is possible you can ask the ECV rental folks, but if you have a day ticket for the park and you have a ECV rented already and you stay in the park when it closes to day guests and switches over to HHN would they let you keep the ECV for HHN. There might be a little up charge perhaps.
3. The outside ECV companies usually drop off and pick up at the Resorts. You can ask if they will drop off at the park and pick up too.
Some of them could have an arrangement with the Resorts to even drop off and pick up at Resorts for non resort staying guests who want to go to the parks.
There are wheelchair rentals as you enter walk from parking garage to CityWalk. I think it is on the left near an I ice cream shop.
There are also wheelchair rentals a in the parks, but these cannot leave the parks.
When going through Haunted Houses in the past they have requested those that can to transfer to a wheelchair from their ECV for family to take through the houses. If that’s not possible you can stay in ECV.
If you want to make your dad’s HHN experience very special and you have only one night. Think about a RIP Tour. This will get you to the front of the line with a tour guide. The information on the RIP tour is on the Universal website under HHN information.
Having said all the above. I would take into consideration your dad’s overall health. If he is in advanced age and has heart or lung issues HHN would definitely be to much for him. It can be very hot, humid and exhausting. Also increased crowds means increased possible exposure to Covid. Which to someone in advanced age with health issues could possibly have a poor outcome.
I have seen young ones exhausted after a night of HHN. Those of us who have done HHN for years know to pace ourselves and not to over exert ourselves before a night of HHN and it can still be exhausting. It is fun, but there is a lot of walking to reach the houses on the back lot.
I wish you well in your planning.
Hope this helps a little.