What's technical difference between official virtualbox and VirtualBox-OSE?

The difference (aside from any distribution-specific patches), and reason that you would get a kernel oops is because the VirtualBox host modules are only compiled for that specific kernel. The likelihood of breakage is high if using another kernel (different symbols, different metadata, etc).

Distribution-specifics aside there is no difference anymore. There were some closed-source drivers in the non-OSE package, but they have been moved to an extra package.

Before version 4.0, there were two editions of VirtualBox: a full binary containing all features and an "Open Source Edition" (OSE) with source code. With version 4.0, there is only one version any more, which is open source, and the closed-source components have been moved to a separate extension pack. https://www.virtualbox.org/wiki/Editions