Hi Chad,

David had submitted a ticket about this - I was able to find it and the reply from the Product Manager for Help Center.

Details are:

Right now you'll need to check the box next to "Display unsafe content" in the "General settings" area of Help Center to get tables to work in Knowledge Base articles.
The fact that you have to do this to get tables to show is a mistake that we're working on fixing right now. (We did not mean to make these tags part of the unsafe tag set.)
The fix should be out in the next few days.
Tables are only allowed for agents writing KB articles. (I don't know if that's the case permanently as content formatting will improve for end-users over time but for now it is).
Only agent can post articles.
We're also planning to make it easier to add tables in articles for agents.

I hope that helps, please let me know if you have more questions!