If the scanner/radio is not specifically prohibited, there's nothing stopping you from placing it at the bottom of your camera bag that has other (permitted/normal) items on top of it or totally obscured by your shirt/windbreaker, etc. If someone went to the time & effort to write out a list of specific items that are prohibited, it is reasonable to *assume* that if a scanner is not listed, it means scanners are allowed & thus you're conducting yourself perfectly within reason (though they can always refuse entry to you without much of a reason).
I know someone who got his Yaesu VX-8 onto Nellis for last year's 'Aviation Nation' (scanners/two-way radios prohibited) last year by putting it at the bottom of his backpack (which was allowed) & then used psychology -- the intentional clutter of numerous reasonable & permitted things in the backpack, and engaging the approx. 20 year old Security Forces Airman in friendly & humerous dialog to distract her focus during the 10 seconds spent dealing with the person & poking around inside the backpack.
Like TSA, it's basically security-theater -- busy-work for the poor SFs dealing with the masses at the checkpoint & ignorant members of the public feeling proud at how 'secure' the installation is, when the reality is often that if you wanted to sneak something on-base, you just toss it over the single fence separating the dirty/sterile areas or get a vendor's pass & hide it amongst the crap for sale that you're bringing onto the base the day before.
As a whole, DOD has their heads up their asses regarding radio-devices -- there's no formal DOD policy, sometimes it's not listed as a prohibited item on the event's web page, but is on the list on a sign at the checkpoint, or vice-versa. If they think that COMINT via a scanner poses a tactical or strategic threat, it's up to THEM to properly secure that info via encryption.
If you want to be a good citizen & follow all their rules, that's great! Just get someone to stream one or more of the base/airshow freqs you want to hear, and listen to them with your smartphone via the stream.
