Again, I don't know the specifics about Windows, so I can't say exactly what a cheater could or could not do. I do know that kernel chaining does work w/ Windows, otherwise the GRUB bootloader would be DOA.

Whatever Windows does is a completely separate thing from Secure Boot, since Secure Boot only impacts early boot (i.e. the handoff from UEFI to the kernel). So getting into what Windows does and does not allow isn't particularly relevant to the discussion about Secure Boot.