I've not had experience training with anyone suffering this particular problem. However, in my view, as long as the student has clearance from a doctor, they should be encouraged to train whatever their 'disability'. Aikido can and should be practiced by anyone/everyone in the spirit of O'Sensei's wishes.
This does however mean that teachers need to be able to adapt to those students who may not be so 'able'.
My own experience is this: I started my aikido training with a man who the medical profession believed 'should not be walking' considering he had had a childhood disease (polio I think) that had left him with virtually no muscle strength from the hips down, that coupled with the fact that early on a number of operations had fused his ankle bones so his feet were left permanently crooked.
He believed that it was his practice of aikido that kept him out of a wheelchair. The mental/physical co-ordination most of us take for granted, for him was a moment by moment task just to stay upright!
Consequently he could not rely on lower body strength to 'power' his way through aikido technique. He developed an increadibly soft and powerful ki lead approach, which I felt on many occasions making ukemi for his demonstration of an exercise.
This of course has influenced my own practice and teaching.
I now have an older lady practicing with me who has ME and osteoporosis, anyone practicing with her has to be increadibly respectful of her physical limitations. She loves the practice and the mental / physical discipline has improved the quality of her life off the mat. Which is, as far as I am concerned, the main reason for practicing aikido.
In conclusion, I would encourage you to welcome him in, and do all you can for his progress. If he can't do particular exercises, so what, he ( and you ) will in time learn to adapt. I think everyone benefits from having the widest range of students practicing.
Just my humble two penneth worth,