This is the conversation:
Originally Posted by Iron Man 2
Nick Fury: Whoa, whoa, whoa. He took it? You're Iron Man and he just took it? The little brother walked in there, kicked your ass and took your suit? Is that possible?
Natasha Romanoff: Well, according to Mr. Stark's database security guidelines, there are redundancies to prevent unauthorized usage.
So yes, it is fully implied that Tony let him have access.
Originally Posted by Loki882
Yeah, totally trust the guy who has shown himself to be an incompetent douche and hates Tony, but doesn't have his talent, that won't backfire at all.
As I already mentioned, he didn't trust Hammer at all. He was ordered to work with him after he already had the suit. Unless he wanted a court-martial, he had no choice but to work with Hammer.