No, being wheelchair bound is not an automatic disqualification for all life insurance, but is an automatic decline for most. Your best bet is guaranteed issue life insurance, which does not ask any health questions at all. However, there are very few options like that for persons under age 50.
If your son is able to transfer independently, it may be possible to get him a simplified issue policy, that asks some (vs no) health questions.
Finally, there are some companies that will consider a fully underwritten policy of any size if the wheelchair bound person is able to handle full time employment, transfer independently, etc. Unfortunately, this would not be your son’s case, so not an option for him.
I wish you and your son the best. Please feel free to contact me to discuss personally.