OCD runs in both my and my husband's family. The key to what you describe is "It doesn't appear to interfere with his daily life as far as I can tell."
Certainly, keep your lines of communication open, but what your son counts may not really get in the way of his daily routine at all... and if it's innocuous, I wouldn't worry about it. However, if he runs to the bathroom to wash his hands, or starts to open his door five times (or fifty) to come out of his room in the morning, it's time to do something. He may actually be "counting" to reduce stress--or even to practice counting--in the same way that kids sing songs they like (over and OVER) to do the same thing.
When I was a kid, I'd walk a circuitous route to school to avoid stepping on sidewalk cracks, and I still have a few quirks that have stuck with me. My brother herded potatoes all over the house, leaving them in rows in the hallway and his bedroom (said it relaxed him), and if we put the potatoes back, he'd go get them and start the process all over again.
Your son might be a bit systematic in his behavior, but unless it has an impact on his daily life in some negative way, I wouldn't worry--and I'd be cautious not to let anyone criticize him for it (not that this seems to have happened yet). Who knows? He might be a math genius some day! :)