You can normally look at the release notes for the different versions, but the version you have was released 2 years AFTER Server 2012 R2 (even the FIRST release was a year after), so there is no real reason why the version you have wouldn't be fine, unless there is an updated driver that would require it, and that information is not easy to find either (release notes … sometimes). Specific minimum versions are not universally available, but I suspect that 13G was not added to the documentation because 1) they don't often update documentation, and 2) they were all released with support for 2012 R2 from the get-go.
Looking to upgrade our R430 from Server 2008 R2 SP1 to Server 2012 R2. All the hardware looks compatible, I just can't verify that the BIOS and iDRAC versions are sufficient.  The following guide only shows up to 12th generation servers. [URL]    Current Versions BIOS - 1.2.6 iDRAC - iDRAC8 2.20.20.20 (Build 41)   Thanks!
R430 iDRAC/BIOS version for Server 2012 R2