I have a son with poor visual spatial and visual perception - similar to your son. Although my son IS dyslexic, these issues are not aspects of his reading disability. Dyslexia is usually described as a weakness in the phonological system and rapid naming domain. While these visual issues compound my son's reading issues, they are not the "cause" of the issues.
Like your son, mine is quite strong in many "visual spatial" areas. He is a master at Legos, has a strong number sense, and very strong comprehension. However, on tasks that require visual motor - especially penmanship - he is very very weak. Very weak!
Some things to keep an eye on as he gets older - the writing component of math can be problematic. If your son does not write legibly, has difficulty lining up his numbers, multi step math problems can become a disaster. Graph paper and or line paper helps my son. Copying from a book or the black board might be difficult. The VT might help this, but I found that my son did not sustain the the skills he developed through VT and over time he was back to square one.
Does your son have OT to address the visual discrimination issues? If not, I'd look into it. Maps, graphs, busy work sheets can be very difficult for kids with weaknesses in this area. OT can help to develop these skills.
