A search for FromDIP() in wxSmith returned nothing.
Fortunately, code generation for wxSize and wxPoint is centralized in wxspositionsizeproperty.cpp and wxsdimensionproperty.cpp. On the other side, wxSmith does not use FromDIP() itself, so it must be heavily edited.
Adding the FromDIP() may break existing wxSmith dialogs, but HiDPI in wxwidgets is so new that IMHO they will not be a lot.
EDIT: FromDIP() was added in wx3.1.0, but we still support wx3.0.x for C::B itself and code generated by wxSmith.