While poking around on rec.gov tonight I found that you can now ask to be notified when campground spots open up. it is a beta feature that only works for front country campsites that have already been released and taken. It could be useful for snagging spots from reservation cancellations. I was able to create a notification request for Two Medicine for a range of campsite numbers and dates.
I noticed this feature last week and set up a request. I received a notification a few days later, and was actually in the process of checking emails when it arrived, so I opened it pretty instantaneously. I quickly went into recreation.gov and the site was already gone.
The notification will inform you of the number of notifications sent out for the particular request. I don’t remember the exact number, but in my case it was something over 800. So lots of people are using this feature and you’ll have to be quick.
This notification feature can be quite useful but as you mention the sites, once open, may be taken quickly. I was able to snag a campsite in Arches NP using the notification last fall. Unfortunately, for high demand locations like Glacier (and Arches) there are a whole bunch of people signed up for the notification.
I’ve only had one hit to date (results in thread), and Rec.gov didn’t register (others did) . A couple weeks later I did have a (suspected phantom) alert from Rec.gov and none of the others.