The finger-pointing likely to result from an incident would make this driver as good as uninsured.
I guess uber has an insurance policy that covers their drivers during rides now, so hopefully that kicked in to take care of your friend.
Everyone should read their insurance policies to know their exclusions.
In the US. It's not clear if they have this anywhere else.
I think that was one of the greatest lies of Uber at the start "just drive your car for money in your free time!" - that's all great, but no private car insurance would cover you while doing that.
Total your vehicle? Personal insurance won't touch it, and the Uber coverage you thought you had is useless.
The only way for commercial drivers to be covered by the same policy is to price the risk of an unknown number of commercial drivers into everyones policy.
All you have to do is be upfront about it, and willing to pay.
Yes, it does cost more to cover employees as opposed to owner/operators of a business venture, but it it is not impossible (if it were taxis would not be able to exist).
What is probably true is the default insurance given out by Uber will not cover people not listed on the policy, and only the person contracted with Uber is listed on the Uber-backed policy.
Beyond that
People driving under other people's Uber accounts don't have a license or are otherwise ineligible to drive for Uber (criminal, underage, etc) otherwise they'd get their own Uber account. Uber literally pays people to sign up as drivers - there's no legitimate reason to drive under someone else's Uber account.
Commercial Insurance would probably exclude coverage for any incidents that happen when an unlicensed driver is using someone else's Uber account.
[0] https://immigration.procon.org/view.resource.php?resourceID=...
Business done without a solid basis is often high risk. That risk unlikely to be worth it.
Finally, as a basic matter of principle, I do not do business with people who are dishonest.
Doing that is on par with debating liars.
It's also IRS fraud, there is no background check, the list of issues with this is just huge.
There are plenty of reasons to care - undocumented people are a legal liability for both the passenger and Uber.