Sure, slicks are fine on hardpack. My normal routes I can do on 25mm slicks, I just gotta slow down and choose my lines carefully a lot. The width&pressure of gravel tires lets me just bomb through ruts and minor potholes with aplomb. What routes I can ride doesn't really change, just the speed and stress vs fun.
But I can almost always find some hardpack to ride that isn't too slick when wet on my routes. YMMV, literally!