Hi simmania,
I just wanted to provide a quick update here. I was notified that the ticket I had submitted for this issue had been fixed and, after waiting for some additional hot reload fixes to be put in place, I ran my test again in our latest internal build. The error message stating that the Blueprint cannot be saved no longer appeared. If you have built the Engine from source code, you can find the commit containing the fix for this issue here. If you are using the binary version installed through the Launcher, the fix will be included in a future release version of the Engine.
As I mentioned, there has been some work done recently to improve hot reloading specifically. You should see some improvements in this area in future versions.