WEBN's website says "No weapons of any kind" at the fireworks. Of course they don't own the park and other public land along the Ohio River. I would surmise that open carry may get you escorted away at best, and perhaps even arrested** for "inducing panic", or illegally being in possession of a firearm, on the Ohio side at least.
I believe that open carriers on the Kentucky side have had less problems in this regard. Also there is precedent for open carry being deemed as legal at the similar "Thunder Over Louisville" event held each year. Pretty sure there are threads on that topic in the Ky. subforum.
**While an inducing panic arrest would be quite bogus, it likely wouldn't keep the arrest from occuring, unless you happened to be in the company of a well known defense attorney at the time or something.
With regards to Cincinnati parks, they still have some of them posted with 'No Guns' signage, in spite of the fact that this defies current statewide pre-emption of such rules.
Bottom line for me would be to carry concealed in this case, partially because I have a CHL, and partially because I have no desire to OC anyplace that has elbow-to-elbow attendance. But it's a moot point, I don't get anywhere near that whole gathering, it's just too much hassle to get out afterwards.
EDIT: Also, I'd do my carrying on the Kentucky side of the river, it seems that most LEOs on that side at least know what 'statewide pre-emption' actually means.