I have a standalone WDS server functioning over PXE. There is no AD environment. I can capture and deploy images with WDS, I just have to put in a name and password every time.
So I build a new share in MDT, and added the share credentials to its Bootstrap.ini:
KeyboardLocale=en-US
UserDomain=WinDeployServer
UserID=ShareUser
UserPassword=SharePassword
It's definitely in there, saved, and valid. Next I right click and "Update Deployment Share" Once that's done, I added the boot.wim from that MDT share into my WDS boot images. But when I PXE boot and select my MDT boot image, it still goes into WDS Windows setup. It asks me for the credentials, and once I provide them, it gives me a list of my regular WDS images to choose from. My MDT customization just isn't entering the picture at any point.