Legally, I think so. Local and federal laws and safety standards would have to be checked. Technically, yes it could be ridden, but with conditions. It will be okay for slow speed riding, however an emergency stop (like when you get cut off) will probably result in in the rear wheel locking and a crash. High speed riding (above 80 kph / 50 mph) could be defined as suicidal.
Safely riding, at any speed, with only a rear brake would be a definite "NO!" in my opinion.
Safely riding, at any speed, with only a rear brake would be a definite "NO!" in my opinion.