Not as many as used to, outside of succubi. Used to be...not quite common? But deals with humans were common enough that it wasn't exactly unusual for a devil to decide a human was interesting like that.

These days, most demons seem to hold humans in contempt thanks to Mundus spreading genocidal attitudes. I'm not sure if I'm the only one left who'd consider it, with Sparda probably gone, but I haven't met any halfbreeds other than his sons.