Intel® Rapid Storage Technology 12.6 may not have it on the release notes; however it is still compatible with Windows Server 2012. However that version has not been officially posted on our web site.
The option ROM itself is implemented by the motherboard or computer manufacturer directly, therefore we do not provide Option ROM updates. The version of the driver should always be equal or greater the Option ROM version.
Based on the 12.5 release notes, that version does not support a mature controller like the Intel® 82801IR/IO I/O controller hub (ICH9R). And so, it may fail to retrieve information from the option ROM of your system. Therefore, it would not be compatible for your system.