DART is not unsafe. Some of the outlying suburban stations might be less safe, but personally, I would not have any problems going anywhere on DART. Downtown Dallas is not unsafe. The DART route between DFW and downtown Dallas runs through some of the richer neighborhoods, so no safety problems there either.

Keep the TRE schedule in mind. If you arrive at a time where you can reasonably catch TRE from DFW/CentrePort station (there's a shuttle to the station from Terminal B) it's faster than DART and is still only a 5 minute walk away from the Fairmont if you get off at Victory station.

DFW is about 30km from your hotel.