You have to prove that the ancestor fought on the side of the American's or did some form of patriotic service for the American cause. Being a Loyalist would be a sure-fire DAR disqualifier.

I myself have more Loyalist (UEL) ancestors than Patriots. Apparently one of my ancestors was married to a Loyalist...after the war, he went to Nova Scotia where he drowned...his wife returned to NY, and later married a man that was a Patriot. Must have made for some interesting dinner converstion.