It seems unlikely. By June ‘44 the US Army had plenty or tested and bloodied units, and one such division participated in the initial Normandy landings. The American assault on Omaha was spearheaded by the 1st Division.

The 1st Division had first entered combat on Nov 8th, 1942 in Oran Algeria. They then participated in at least a half dozen major battles as they fought across North Africa, including the hard fight at Kasserine Pass. To follow that up, they participated in the landings in Sicily, fighting their way across the island. After that they were relieved and sent to the UK to rest, refit, and train for Normandy. The 1st already had nearly 2 years of time overseas, including about 8 months of direct combat experience.

The 1st was far from the only experienced division by 1944. Even if the US felt the need to leaven out the green units, they had plenty of experienced US soldiers to do it with. There would have been no need to use disguised Allies. They could have pulled in troops from the divisions that had been fighting in Africa, Sicily, and Italy.

That said most of the US units on D Day were green. The 1st was the only experienced full division the US deployed in the initial landings. But the experience of US troops wasn’t considered a primary concern. There were experienced troops sitting in the UK. The 9th Division for example had also fought in Algeria, Tunisia, and Sicily. But they didn’t cross the channel until June 10th. They has been reserved as a later reinforcing group and were used to secure the Cotentin Peninsula and to capture the port of Cherbourg. While green, units like the 29th Division had been training for more than two years at that point. And that training included lessons learned by the bloodied units that had engaged in combat. So there was no real worry that the unbloodied units wouldn’t perform.