First of all, the role of that executive would require a business need to access the data at all. Banks are really big on compartmentalization and the most important principle is that a bank employee can only see, let alone modify, data as far as it's required to do his or her job. This also applies to top executives.

It's unlikely that an US top executive has a valid business reason to see Swiss data when visiting the country. If such a reason exists he can surely see it, but it's probably illegal to take the data out of the country in any form. (I'm guessing here, but Swiss criminal law is quite finicky on the issue of bank secrecy).

If the top executive tries to asshole his way into the data (as in: "hand over the data, or you're fired") any halfway smart employee would immediately inform compliance, where a whole cacophony of alarm bells would go off.

As for IT professionals. Sure, a lot of foreign IT professionals work for Swiss Banks. But the need to access actual customer data is very, very rare. If the need exists, they can surely see it, but only from within the country's borders.