Hey Karah!
I'm so sorry your husband has had such an awful experience, and I do hope that he continues his journey towards healing.
Neck gaiters are permitted in this context at
Walt Disney World. The restriction on neck gaiters referred primarily to their use as a face mask, but to use them as your husband would need to is completely appropriate. For information regarding the current face mask policy and other protocols for health and safety, you can keep an eye on the
Know Before You Go section of the Disney World website.
I would strongly encourage you to reach out about Disney's
Disability Access Service to see if your husband would be eligible. The service is designed for guests with a disability which makes standing in a traditional queue for a long period of time a bit more difficult. While many of the attraction queues are undercover, and some are even indoors, there are still some that would require your husband to be outside for an extended time. If he could get
preregistered for DAS, which you can do 30 days prior to arrival and up to 2 days before your arrival, it would allow you to plan return times for attractions so that he wouldn't have to stand exposed to the heat and sun. Even under shade, the heat can be intense. He could relax in a cooler, shadier spot or even do another attraction with an indoor queue while you wait.
Also, consider using the Disney Genie+ service. This added option to your tickets also gives you a return window, making it so that your wait time is shorter.
Happy planning, Karah!
Anna