I would disagree. American generals have experience with drawn out conflicts versus the short, decisive wars of Europe (Crimea aside). Depending on what nations are looking for, having experience in multi-season campaigns that would be impossible for most European nations to provide.Don't forget that Europe saw a lot of wars. Sure, the officers who served in the ACW would have valuable experiences - but not really anything better than officers who served in the Crimean War, the Second Schleswig War or the Austro-Prussian War, for example.
Of course, the challenge is finding someone who takes “These guys can teach us how to fight long wars” over “These guys can teach us how to end a war quickly.”