Phillip Haythornethwaite says that the regiment "was formed in September 1810 from the Royal Dutch Hussars and the Dutch Garde du Corps with a strength of 748 men. The regiment was increased to 1,400 by 1812 for the russian campaign ... from which barely 200 returned. In January 1813 the regiment consisted of eight squadrons each of 250 men. Two more squadrons were added from the Paris Municiple Guard; by this time only the first four squadrons were composed of Dutch, the remainder being French. The regiment was disbanded on the abdication of Napoleon in 1814, four squadrons being taken into the new Royal Guard. during the 'Hundred Days'campaign these four squadrons were placed with the squadron of Polish Lancers in the combined regiment of Chevau-Legers-Lanciers of the Imperial Guard".

I don't know which squadrons were taken into the Royal Guard, and of course any losses after 1813 would probably be replaced with Frenchmen, but it seems possible that there were still a number of Dutchmen in the ranks.

In terms of loyalty I think there would be a distinction between an Imperial Guard regiment, and a regular Dutch regiment.
When The Netherlands changed their allegiance many soldiers despite their personal beliefs would have gone were the army sent them, as soldiers do. But for some, and particularly for the Guard their loyalty to the emperor may have been higher, Napoleon was after all famous for being able to engender fanatical loyalty in his troops.
Any of the 200 survivors of the Russian campaign who were still around in 1815 would, I think, be as loyal as their Polish comrades.