Is Jackson a good middle name for Oliver? Worried about initials being OJ.?

Oliver Jackson sounds great together. If you like it, that's all that matters. Most likely, there will be plenty of other things going on in the world by the time he's old enough to be affected by it, that OJ will be ancient history anyway. You have a good reason for giving your son that middle name and you obviously like the first name, so go for it.