To further the mystery, Vanicek notes in 1814 1 Wallachian (1 bat) with Cobourg and 2 battalions of Wallachian-Illyrian with Hessen-Homburg as shown in the OOB link you provided. No other Wallachs with the Army of Bohemia. This OOB shows "Tirailleurs" with Franquemont but doesn't ID them. Your other source identifies them as "French" Tirailleurs Valaques.
Running through Nafziger's Wurttemberg Army, we can match all ten infantry regiments and the four field regiments of cavalry as those with Franquemont. Missing are only the guard (understandable), some of the new Landregiments (militia) and the Landscarfschützen Regiment Hall. I think this last is most likely your tirailleurs. Maybe a handwritten Hall was mistaken for Wall.? It's not proof, but enough to call the ID into question. Scharfschützen would translate to tirailleurs.
The incorporation of French prisoners also seems odd. It would be unusual for prisoners to be armed and sent to fight their own countrymen. It might be that French "prisoners" were not French at all but Wurttembergers who had been captured by the allies when they were still fighting alongside the French who were repatriated to fight against them after Wurttemberg aligned with the allies. or even Germans serving in French regiments (from annexed north German areas maybe?) who had been captured or deserted and were entirely willing to kill Frenchmen. At any rate, it sounds like there is a good story there, it would be interesting to dig up some more details.