Clover is non-native in my area. I've witnessed native bumblebees visiting clover, but they show a much stronger preference for larger forbs, both native and non-native. For one, they can't nap on clover (too small, I assume, even when allowed to grow to full size). Additionally, I haven't seen pollinators other than honeybees and bumblebees at the clover, whereas other flowers attract dozens of various species (as well as their predators, creating a fuller ecosystem).