Samsung S5 compatible with tracfone and Verizon Wireless
After having gone through this process, it seems that all Verizon-compatible Samsung S5s are compatible with TracFone, and there is no unlocking that needs to be done. All I had to do was get the new SIM card from TracFone and put it in the S5, then follow there instructions to get it activated. AFAIK, I could go back to Verizon at any time, by simply putting the old Verizon SIM card back in.

For any other model phone, just contact TracFone. They'll tell you whether the phone is compatible or not. It really was a straightforward process.