For my vcenter 6.0 it appears in the other patches, not the critical. I believe for 5.5 you will get a single patch rather than 2.
OK. But I'm not seeing *any* patch later than December, not in critical, not in non-critical. The latest "critical" patch I see is 2017-09-01; I see no critical patch with a date in 2018, nor any non-critical patch.
Do I need to import the patch, the way I do with OEM customized ISOs? I do see green checks for "Check for new notifications", so if was released, I would have thought I would have seen it ...
If your not seeing it in your update manager then manually download the patch and import into update manager, it released on the 9th.
Instructions on how to import into Update Manager.
Be aware that the full fix for the big involves multiple steps, you need to update your ESXi hosts BIOS, patch ESXi, Update VM Hardware Version and Patch guest OS.