Can you use boot camp on a 5,1 Mac Pro 2012?

NO.

Not supported by apple.

Installing Windows via USB installers is not recommended as it has managed to mess up some people's Mac Pros as it tries to install in UEFI mode which can harm the firmware.

Installing off an optical disk runs in legacy mode.

from:

https://blog.greggant.com/posts/2018/05/07/definitive-mac-pro-upgrade-guide.html#windows10

Hi,

You can run macOS as well as Windows on your MacPro, also you can run Windows as well as macOS at the same time with the utilities like VirtualBox, VMware Fusion, and the like.