Yes. You should be able to combine a CDP code, a coupon (PC#) and a special rate code at will. In fact when I use Hertz's Web site I usually have one of each.
Only exception I know of is that some coupons can only be used with certain CDPs -- for example a AAA coupon with an AAA CDP, or a frequent-flyer-program coupon with that airline's CDP.
[This message has been edited by Frequent Freak (edited 12-05-2001).]