In fact I believe it was supposed to be a Rommel Afrika Korps uniform.

Taking the piss out of the Nazis by dressing up in one of their comical uniforms has been done before often enough. It's generally understood as an expression of contempt rather than admiration.

However the whole idea of a Home and Colonial party with an African theme seems a bit distasteful, largely because it's only too likely to be seen as an expression of nostalgia rather than contempt.

Maybe he'd have done better to dress up as someone from the North American Colonies.