The engineer, says Bloomberg, is Ruben Caballero according to a source cited tin the article. It's also reported one of Apple's carrier partners also questioned the performance of the antenna design.
Apple has declined to comment on the report, and Caballero isn't responding to calls and emails. He might be busy checking those Silicon Valley help wanted posts. A quick check shows a Ruben Caballero of San Jose has several patent applications for antenna designs, including one that is a design for a "handheld electronic device with conductive bezels." Sounds familiar. The Linkedin site lists Caballero as a Senior Director, iPhone/iPod at Apple. He's been there since 2005.
It's not unusual for a design team to have differences of opinion on technical matters. I've been through a few of those meetings myself. In light of the current storm of controversy over the iPhone design, those conversations take on added importance.
You can bet Steve Jobs will be asked about all this at the news conference tomorrow at Apple headquarters.