This 3rd party is comprised by OpenBSD developers though. While not an official OpenBSD project, the people that provide these patches are the same people that have built OpenBSD packages in the first place. So if you trust those binaries, you should trust these binaries too.
This is simply outdated and wrong information. M:Tier does not employ "the same people that have built OpenBSD packages in the first place." Last I checked, naddy@ built the AMD64 packages. He does not work there. In fact, I don't know if any OpenBSD developers still work there. Maybe one (jasper@) but you'd need to ask them.
Thanks for the important correction. It would be great if this were documented somewhere.