MEL
In answer to your question. Yes the Wheel Fire Detection System in accounted for in the B737 MEL.
You can dispatch with it inop, provided the BTMS (Brake Temperature Monitoring System) is operating normally. Or if BTMS is not fitted (or inop) then the brakes must be cool to touch before engine start.
Also, after takeoff the landing gear must be left extended for 10 mins (unless engine inop climb performance and/or ice accumulation is a consideration).
There is also a increase in fuel and trip time to account for the delayed gear retraction.