The BSD-style kernel "subsystem" of XNU, Darwin's kernel, is statically linked with Mach and executes in privileged mode. So, while it "has" Mach and some parts of the kernel interact with other parts via Mach port interfaces, XNU isn't really a microkernel as classically defined anymore since it provides all the facilities you'd expect of a non-micro kernel.

It's been a while since I have kept up with the kernel space but I remember when I last was interested in it, that there was a trend toward hybridization. That Linux was adopting some micro like architectures as well as windows. OSX probably could be considered a hybrid from the start.

OS X was built on Mach 2.x, which was pre-microkernel. And the modern XNU isn't microkernel-like at all.

Actually I believe that's incorrect: stock Mach 2.x was considered a microkernel (though, like Mach 3.x, not always used as one in practice), and, versions of XNU since the first client release of Mac OS X are built on a modified Mach 3.0 kernel. But you're right that it's not used in a microkernel-like way.