I think you need to have a look at what your app will realistically scale to before worrying, and if you believe the problems will be real, then take appropriate actions (whatever they may be).
First, let's look at your app in isolation. From your description, I don't take that there will be thousands of people advertising at the same time. Let's say about a hundred vendors all the time, and the visitors for a few seconds. Considering the effective radius of BLE advertising, especially in a RF noisy environment like a conference/expo floor, you needn't worry about scaling - realistically.
If it happens that you are in a small area with thousands of people using your app to advertise, then all the advertising channels will get saturated, and that will be the end of that.
But, let's look at the reality of such an environment. You will have thousands of people, all of them with smartphones, some of them with other additional RF noisemakers like smartwatches, tablets, BLE keyfobs, and such. All of these are advertising, all the time. Some are connecting and communicating - all this happening in the same frequency band as WiFi. Things still manage to work, when they do.
I think your main issue will be, scaled or not scaled, discovery while moving. When your app is in pockets/handbags, the devices will be in low power passive scanning mode, and discovery will be slow. May be too slow for walking by a booth, or two attendees passing each other.
The range provided by iOS devices in common use situations is bound to be less than dedicated iBeacons power tuned and strategically placed. While this will work to your advantage by not casuing too much interference, a smaller radius will be easier to walk by without your app detecting anything.
Food for thought.
