Southwest employees, parent, spouse, and children all have unlimited free travel. There are no taxes. We can pretty much get on any plane at any time given there is an empty seat. It's actually one of the major perks of the job.
We also get 16 buddy passes per year, which are free standby flight coupons that we can give to anyone. The only fees associated with that are the income tax on the value of the passes ($40 each).
We also get to fly free on a number of other airlines as well through local agreements, as well as ZED or ID fares with pretty much every airline in existence.
<<-- Notice my avatar. Being a Southwest employee is the ULTIMATE flight loyalty program
Yes, fare paying passengers are always given priority. A non rev should never displace a ticked passenger unless they are must ride (crews needing to be somewhere for work purposes).