Yup! We support down to Windows 7 and Windows Server 2008R2. You just have to install the bits from GitHub (but they're actually more up-to-date because we can ship there a lot faster).
Probably not. The Windows Subsystem for Linux was introduced with Windows 10.
This is a win32 port of OpenSSH, it does not use Windows Subsystem for Linux. WSL can already run Ubuntu elf-binaries of ssh.