I've bought quite a few premade dowels over the years that were oversized a good bit from what they were listed. Depending on the thickness and moisture content of the wood you're drilling your dowel holes into, it may or may not be a problem.

But what I usually do in these cases is just shave a flat spot on the dowel. That way, it has room to expand, should it need to. So long as the wood it's going into is thick enough not to crack if the dowel expands, it'll deform the dowel somewhat as it expands into the space created by the shaved edge. That's my theory anyway. And so far, it's held up.

Sometimes is the dowel is really thick, I'll install it into a drill chuck and sand it down, run it through a doweling plate, or just shave off a bunch of corners with a spokeshave to get it back down to size. It should be a tightish fit. But you definitely don't want too tight. Don't worry too much about the expansion created by wood glue. Once the glue dries, it'll shrink back down to size. It's the expansion that happens after that that matters.