In answer to your question,Yes!
I cant say "every" but I can say "most" Autistic children can be taught to swim unless they are severely disabled.Even children with physical disabilities are capable of learning to do physical activities that non disabled or non handicapped children are capable of doing.Autistic children often need to be taught differently and they may take longer to learn,but there is no reason they shouldn't be taught even if it means spending every lesson for a period of time just getting acquainted with and comfortable in the water. Learning to swim, is more possible and a lot more likely than it is impossible and unlikely.
Most Autistic children are drawn to water even though they can't swim and normally would refuse to get into a Pool.Like any Neurotypical child,Autistic children are going to be more curious than cautious about a large body of water when they are alone or unsupervised.
Please take every precaution and please don't ever assume that your child's intense fear of the water or his inability to swim will keep him at a safe distance from water and prevent him from drowning,because it won't.