Tychus new talent Melting Point doesn't appear to do bonus damage to summons.
Summoned units are summoned units, produced by a hero's ability or trait. Monsters are skeletons, immortals, punishers, web weavers, garden terrors, and zergs, produced by map objectives.Fuente
This is intended. Summons are their own separate category, and should be listed as such in any tooltip that does extra effects to them (most commonly they simply fit into the Non-Hero category which naturally would include them).