Do you need to UL Certified the enclosure with the board inside?

The Raspberry PI is not UL approved, to the best of my knowledge.

The original intent was not to have any certification done at all since it's essentially a development kit. However, things changed and they were forced to do some EMI and ESD tests to get CE certification , which they successfully did.

They're OK for CE, FCC and C-tick approvals, but not UL. Don't be surprised if UL doesn't want to do a full investigation, including the Pi. You'll likely also have to guarantee that your setup will use an approved power supply for the Pi.

Usually, "UL" certification for industrial control panels refers to UL/ETL 508A Listing or Recognition. There are other organizations that perform compliance testing to the UL/ETL 508A standard, although UL is among the best known (and often the most expensive).

It is not possible to obtain certification to 508A unless all components are Listed or Recognized or a certification/verification is obtained at the assembly level. You can have your industrial control panel and Raspberry PI verified and stickered in compliance with UL-508A as an assembly, provided that your design meets the requirements of the standard.

Generically speaking, it is possible to achieve compliance without every component being UL/ETL recognized if the device consumes less than 200W and is mounted in a Listed enclosure. Check the standard for the fine print. At the end of the day, you'd have an ETL apply a serialized sticker to each panel you make that indicates that it was found to be in compliance with UL/ETL 508A, without having UL certify your panel as a standalone product.