From above your quote:

> The only officially-supported operating system is OpenBSD, as this has considerable security features.

And below your quote:

> This is possible (I think?) with FreeBSD's Capsicum, but Linux's security facilities are a mess, and will take an expert hand to properly secure.

It is portable in the sense that it compiles and runs, not in the sense that it has the same security features.

I'd love to see pledge/unveil on (upstream) Linux - but I'm not holding my breath.