It depends on the objects, I assume. If you modeled a bunch of cubes, it would probably be fine, but I tried it with a bumpy blob thing, and there were little wedges and cracks all over the place from misaligned brushes.
It's actually possible to get into Q2. You have to compile the mesh into a Q3 map, then decompile it, then recompile it as a Q2 map. But like I said, it's not perfect. You'll likely have little cracks and slivers all over the place. I've been thinking out a better algorithm for converting meshes to brushes, but like just about everything else, it's far from completion.