Is Imprint MT Shadow pre built into Photoshop?

As far as the license issue, it has no restrictions that would prevent you from using it for a logo.

To quote from Microsoft's FAQ:

"Can I make a company logo using the fonts?

Unless you are using an application that is specifically licensed for home, student, or non-commercial use, we do not restrict you from making logos using the Windows-supplied fonts."

Imprint MT Shadow was never part of the Adobe Font Library, but as @Bobby Henderson has mentioned, it is available as part of most Microsoft Office installations on both platforms. This is where you would have gotten it in the past. What is your platform and OS? If you have a Mac and you are not seeing it installed, you might have to dig a bit to find it, but it is there.

Imprint MT Shadow has never been (at least as far as I can remember) bundled into a fonts collection with an Adobe application. A number of other Monotype "MT" fonts have been included with applications like Illustrator and PageMaker (we're going way back to the 1990's here). Photoshop on its own doesn't have a history of including any sort of bonanza worth of fonts goodies.

The Imprint Shadow typeface has been included in fonts bundles of various releases of Microsoft Office. If you're using MS Office currently or have used it in the past that is most likely how the font wound up installed on your computer system.