That second license thing was from an era when having a USB key die meant you could be down several days waiting on a replacement license file from Limetech. It was meant to allow you to keep a ready backup so you could be up and running instantly vs. waiting.
Now that key replacement is online and automated, having a second license unused on standby is no longer really needed.
The discounted license was never really MEANT to run a second server, but of course you could.
Now, I'm not a Limetech employee, and they surprised EVERYONE with a black friday / cyber monday license sale last year, so anything is possible in the future, but for right now, it's just posted prices.