I am tasked with updating a SQL Server 2012 from a version(11.0.5623.0) before SP3 all the way to SP3 CU2. Can I install both patches without a reboot until afterwards? All the documents I have found on Google indicate that a reboot is only needed if a file is locked.
You should only require a server reboot if something is locked, correct.
However, during the patching, the SQL service will be stopped, patched then restarted so you'll actually be bouncing the service itself twice. Once for the SP, then again for the CU.