I assume the recipe also calls for you to cook it?
I'd say bring it to a soft boil and cook for 20 min or so, stirring constantly.
Ketchup in the recipe doesn't surprise me one bit. Many good sauces are ketchup-based, or a combination of ketchup + tomato paste. The brand of ketchup will make a difference though. I'd recommend DelMonte (not the best ketchup, but makes good sauce).
I don't have any particular knowledge of what's in Gates' sauce, but that all looks about right for a decent BBQ sauce, except you might need to add some water if it comes out too thick (though with all that vinegar it's probably ok).
good luck!