Yes and no, the front heat shield between the XG750 and XG750A have the same part number, however the rear shield between the 2 bikes have different part numbers. OEM part numbers for the exhaust pipe shields are HD-65400103 (#21 in pic) for the front shield, and HD-65400287 (#24 in pic) for the rear shield. If buying new from the dealer you will also need 5 clamps and their part number is HD-65900006 (#31 in pic). All of those parts come out to about $110 plus tax and shipping from New Castle Harley Davidson's online store.
If you are also missing the exhaust shield that covers the catalytic converter, then you will need to order the following parts as well:
1x HD-65400397 (heat shield #25 in pic)
1x HD-50500966 (heel pad #17 in pic)
2x HD-4858M (screws for heel pad on top of heat shield #2 in pic)
2x HD-65900005 (exhaust clamps #30 in pic)
Buying all of these parts new online from New Castle Harley Davidson will cost around $60 plus tax and shipping. You can check with your local dealer but chances are they will have to order the parts in anyways, so I like to use New Castle's site as it cuts out the middle man and cuts down shipping time.
Could the XG750 rear shield fit on the XG750A? After looking at the parts diagram and part numbers, the exhaust pipe itself is the same between the XG750 and XG750A, so I would say there's a decent chance they are interchangeable, but haven't tested it myself. I look at it as there's less than a $50 difference between a maybe on some used shields or a sure fit on some new ones.