First of all, let's be clear on a specific point.

No bicycle without a front brake is safe on open roads. That's compounded in hilly terrain, even for skilled riders who only use the brake as a backup.

My experience riding fixed in hills is that I have three basic approaches.

1- for hills where the terminal velocity is safe, and within my controlled cadence range, I find I maintain better control when pedaling to apply power, albeit nearly zero. My pedaling habits are conditioned that way so my cadence is smoother and my control better.

2- for hills where I want to control speed, I resist pedal, by consciously apply reverse torque in small bursts when the pedals are horizontal. This is a learned pedaling method, and takes some time to master so it can be done reasonably smoothly. I combine it with relaxing, so overall my legs become a source of drag and I manage speed that way.

3- on steeper, faster descents, I do something that seems illogical, pedaling to go faster, while applying the front at intervals as a speed check. This may seem counter-productive, but as mentioned earlier, my pedal action is smoothest with highest top end cadence in power mode, so I see little choice.

Actually there's a 4th option, for when there's a safe visible end to the descent. Here I'll pedal applying power and riding faster than otherwise, knowing the change in terrain will bring it all home safely.