Will humans and animals be harmed by frequencies outside their hearing range?
The only sensible answer to these questions is "sometimes". 

The reason: even a simple monotone must be described by both frequency and amplitude. Any frequency can cause harm with enough amplitude, and any frequency can be harmless when the amplitude is low enough. If you want to actually quantify the damage, you'll need something like an equal-loudness curve, but for damage rather than loudness. As a proxy, you could use the pain threshold of the equal-loudness curve. 

As for the second question, there is nothing magical about 20kHz: physical damage will always fall on a spectrum, there is no single frequency and/or amplitude at which damage begins. If you set an oscillator to constant amplitude and slowly turn up the frequency, you'll notice that the sound slowly dies out around 20kHz. The damage threshold will behave the same way.