I'm not sure why you wouldn't be able to have more than one docked ligand. If you have a viable structure with two docked ligands for instance, then it seems like that'd be fine.
Now, if you're asking if it's safe to use a docking server to generate a structure with multiple docked ligands instead of one, that may be more problematic.
Can you elaborate on the problem and your concerns? If we have more info, we may be able to offer more help.