Unless you are running Slackware64 on a Apple-labeled computer. This would violate Apples OS X Software License Agreement; to whit: "A. This License allows you to install and use one copy of the Apple Software on a single Apple-labeled computer
at a time. (bold is mine).
That said, it can be done.
Boot up takes a few seconds. Doing a shut down or reboot results in a kernel panic and requires the virtual machine to be manually powered down. The OS cannot be updated, updating the OS results in a kernel panic. Other updates can be done, just the OS cannot be updated. Outside of those issues it run fine. Bottom line, you want to run OS X, run it on an Apple-labeled computer.
I will not disuse the details as it would violate the forum rules. This post is probably borderline as it is.