My profile is up-to-date, although maybe I should add the caveat that my opinions are merely my own. :)

Of course.

Though I'm sure you are not the only Microsoft employee who has used OpenBSD.

At one point, after the Danger acquisition, Microsoft HR was advertising a position for a NetBSD developer.

Are there any rules about using a non-Windows OS in the office? Even if it increases your capabilities and productivity?

No, there aren't hard rules against it. Practically, however, it's not very useful to use a non-Windows OS depending on which team/product you're working with.

For instance, Macbooks are really common on some apps teams. In contrast, I work on the OS itself, so tools such as WinDBG and Hyper-V are essential to getting work done.