Talking about the matchmaking 1v1 mode that was implemented:
Do neutrals spawn in that mode?
I could not test it for now.
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Sign up to join this communityAll neutrals spawn as normal
Only the mid-lane spawns creeps. All neutral creeps spawn as per usual and so do the runes. There is only you and 1 opponent against each other. (source) (Not an official quote)
However the first rune does not spawn (source).
On Reddit they explain why there are neutrals: consider it a practice mode.