The simple answer, it appears not to be illegal.
So what about the difficult answer? Here starts the discussion. feel free not to read on if you dont want an opinion.
In all likelyhood this event will have planned for security most likely coinciding with Law Enforcement. Open Carrying at this event will more than likely draw police and security attention. So you have to be ready for that, and the likelyhood that irregardless of the law and work of Open carry, you may get treated illegaly and poorly be LE. False arrest, trumped up charge, etc. Or they might have been trained and know about OC, and just E check you, scowl and let you go.
Have you OC'd before? Have you OC'd in this area before the event?
Do any of the local LE officers know about OC in your area? Have you contacted any senior LE officials to chat about OC? Have you applied and been turned down for a ccw? Do you carry that denial with you, along with pertinent court cases and docs regarding the applicable penal codes? Will you have civilians accompanying you with video backup? Will you have multiple recording devices on you? Will you be carrying sterile?
All of these things are going to affect what happens. Do you want to cause a media stir and get publicity? Cameras and news may be there as well. Are you prepared for dealing with them? Do you have prepared talking points for media cameras, and that they may slant your interview negatively?
I looked at the map and did just a quick cursory check the area does not appear to be in a GFSZ, but that doesnt mean it is, there may be a private or moentessori school I missed, so you might want to do some serious research on where all the schools are and if the area is safe to carry in.
With AB144 still on the Governors Desk many believe any OC if done at all should be very low key until we know where we stand. For this short time period while we wait, any negative press that gets to moonbeams desk might affect a decision. OC'ing at a large public event has potential to cause problems for you personally and the OC movement as a whole. These problems can mostly fall in the bad category unless you have made preparations and smart planning like I listed above. With all that being said, if you want any more info on the above questions let me know I have dealt with all those already.
If you go, good luck, be safe, be smart, come back and tell us how it went.
p.s. (I suggest if you get video of LE interaction or E check, DONT put it on youtube or the net unless it is an amazing positive supportive LE encounter. Bad or neutral encounters dont help us, they can just be used against us).
FWIW IMHO.