I've been doing some tests manually adding SysWOW64 support to a WinPE. Using Windows 10.0.15063 (Build 1703) and Windows 10.0.16299 (Build 1709) source files, Windows 32-bit programs work without running either of these executables.
On older source files, including Windows 10.0.14393 and earlier versions, 32-bit programs will not start and an error message is displayed -
EDIT - Running setwow64.exe in WinPE resolves this issue. As does adding a loadwow64.exe entry to the "ControlSet001\Control\Session Manager" key > with a REG_MULTI_SZ "BootExecute" value > containing data "loadwow64.exe"
The application was unable to start correctly (0xc0000034). Click OK to
close the application.
Information about these files is a bit sparse.
Noel in his microWinpeBuilder project appears to have created an alternative using a powershell script. In the documentation he states -
The 'MonSetWow64.PS1' script
I replaced the "SetWow64.exe" program by a PS (rule 1) 'MonSetWow64.PS1' script. It includes two features:
• Launched without parameters, it allows to visualize objects in the system (like winobj) in a 64- bit system.
• With the 'create' parameter, it creates 2 necessary objects.