SQL Server Installer Update Cache management
Solution 1:
No, it is not: https://support.microsoft.com/en-us/kb/969052/en-us
I ran into something similar on a Windows XP machine when deleting Windows Update files, and essentially broke my .NET installation in a way that required a full reinstall to correct.
I saw another person on the Microsoft forums who was planning to offload the files to a SAN for day-to-day performance improvement, then move them back incrementally if updates failed. They didn't provide a follow-up with success or failure messages, however.