Not having a personal auto policy doesn't necessarily always categorize you as high-risk, but potential insurers will see your lack of one as a lapse — which will, in turn, make your rate more expensive. Learn more about how a lapse can affect your premium here. Generally, insurance companies will not accept business or commercial insurance as proof of prior insurance.
The owner of the trailer would need to add you to their policy if you will be pulling their trailer regularly. If you will not be pulling it regularly, you should be covered — but I recommend you check with your specific company for policy details to make sure. If you have any questions, don't hesitate to ask.
Since the damage is being covered by the company's commercial or business policy then he doesn't have to notify his personal car insurance provider. However, the car accident is still likely to show up on his driving record if a police officer wrote an accident report and his information was recorded.