Indoor Rowing app shows Stroke Rate of zero all the time.

If you are talking about the „built in“ Rowing activity: I am using it too. If it has not been configured differently compared to standard, it should simply log the stroke rate, when you start and stop your activity. No additional settings needed.

Does your FR count steps? Do you run with it and does it show cadence for those Runs?

I am talking about the built in Rowing activity. 

My FR does count my steps. I have not run with it yet so I don't know if it shows cadence or not.

Hmm, if it counts steps, the accelerometer seems to work.

Maybe you should try to reset the activity. Navigate to the activity on the watch, open the activity settings, somewhere should be a reset option for it. Also restart of the watch is never wrong 

Just chatted with a user reporting this issue; had the customer reboot their watch, (top left button for 20 seconds, ignore the message about incident detection and let the watch power off on it's own). Then had the user power the watch back up and that seemed to resolve his issue. Would be curious to see if that resolves your issue as well.