Former Uber engineer here.

AFAIK this is the right answer.

Uber uses fingerprinting to prevent large-scale fraud--smartphones used to load thousands of Uber accounts for the purposes of money laundering or testing stolen credit cards.

On a smaller scale, fingerprinting can be used to make sure that "New Account" related promotions aren't given out to folks abusing the system.

So no, nothing shady is going on. Device fingerprinting here is being used to prevent others from doing shady or fraudulent stuff.