you -could- ride a suicide hub, but it's called a suicide hub for a reason. it would be insane to ride a suicide hub with no handbrake because if you backpedal hard enough, the cog -will- unscrew and you will not be able to stop.

if it is a fixed-gear hub you will easily be able to add a lockring. if it's just a hub threaded for a freewheel (for a road bike) you had better get a new hub, or a new wheel, or a brake.