Absolutely fine, I kept a male Betta and Sparkling Gouramis together in an Arc Tank fine, kept them in an Aqua One 320 and again in a 260L tank, different animals each time and never once had a problem.
So long as there is plenty of decor, the gouramis do go up for air but dont generally live near to top of the tank where the fighter patrols, they mooch about in the plants.