Say the PC sneaky scout has the spell "message" active. The PC has detected an enemy and whispers the presence and location of the enemy to other PC's via the spell. The enemy gets a perception check of DC 25 to notice the whispering, succeeds on the check, and becomes aware of the scout. If the enemy wants to attack the scout, regular combat initiative begins, since they are both aware of each other.
But would the rest of the PC's party (on the receiving end of the whispered message) get a surprise round, since they are aware of the enemy combatant, but the enemy combatant is not aware of them?
What if the scout had reported the enemy's presence and location to the rest of the party long before, and was only detected by the enemy while trying to sneak away?