Why are you referring to them as two separate trips? Are they separate award tickets? How long is the layover in DFW? I don't see any reason why you couldn't check the bags all the way thru from RDU to OGG and then only pay the bag fee once. Or did you plan to pick up the bags at DFW and keep them w/you overnight in DFW - if that is the case, then yes, you will have to pay the fee again.