People have been using IFTTT to connect Fitbit and SmartThings for awhile. See:
The SAMI piece is new. Fitbit was one of the first devices Samsung mentioned in connection with SAMI back in 2013, but as you probably know the official SAMI accounts announcement just came a month or so ago.
http://community.smartthings.com/t/smartthings-open-cloud-the-artik-chip/16548In the week of June 20, as @keithcroshaw noted below, SmartThings added a new SAMI smartapp to the MORE section of Smart Setup in the mobile app, marked “alpha,” and the Fitbit device handler you mentioned, so it looks like they’re preparing for SAMI integration.
I’m not sure if you need a SAMI account or not.