Yes it is. They also had a system for dispensing them from balloons. This was the reason for the balloon fire bombing tests conducted in 1945. The fire bombs would result in reports in US newspapers which would give the Japanese intel about the effective dispersion of the balloon based bombing system.
Not really. Human cleanliness has progressed a long ways since the dark ages. Since the disease is not easly spread from person to person, and it can be treated, it would have caused some havok and some loss of life but would not have been "devestating". Even the tests in China did not prove all that successful.
The bombs were designed to fall slowly and burst well above the ground, spraying fleas over an area. The biggest technical issue was keeping the fleas from freezing (which kills them).