If my child is hit or has a frightening experience, do I need to make them endure it because "it can't be helped due to the disability"?

There's no need to make them endure it. No matter who the other child is, first receive your child's "I was scared, it hurt" feeling and secure safety. Don't dismiss it with "it can't be helped due to the disability"; share the facts with the teacher and think together about preventing recurrence. Rather than blaming the other child, the constructive stance is to seek a form where both children can be safe.

For a child, you could say: "It hurt and was scary, wasn't it. You're not to blame. Let's tell the teacher too."