I know of no reason you couldn't. I did the same thing with my pickled cauliflower recipe. It calls for a handful of onion wedges in each jar, and those are my favorite. So, I just made up some jars of pickled onions in 2008, and they were great that way.

I don't think it's a food safety issue with that much vinegar, and I doubt that celery is much different from cucumbers in terms of food safety anyway.

I think you can pickle pretty much any vegetable if the brine is acidic and salty enough to preserve it safely.

That is a relatively weak brine so I'd recommend making it stronger. Check out the info in the post just down the page called "question about peppers at NCHFP".

Dave

Dave where are you getting the idea that is a "relatively weak brine?" The standard pickle brine is two parts vinegar to one part water. For example, in my "Ball Complete Book of Home Preserving" on page 322, the recipe for Jardiniere, which is a mixed vegetable pickle, (including green peppers and celery) calls for 4 cups vinegar, 2 cups water and 2 cups granulated sugar.