When trying to coax a way to find out if spectators were still detected by ocelots and rabbits i placed a creeper to try and hide in, upon switching gamemodes the mob vanished from sight. I proceeded to fill a hole with various mobs including a guardian and silver fish which could easily be overlooked. I took step by step pictures of what i did to get them to vanish from the start to end. All mobs (overworld) i tried all disappeared as if i used peaceful ( i didn't) when i executed the command.

I explained it well in the pictures in my opinion, but to recreate it for those who couldn't read the pictures it goes simply as said below:
1 Spawn a Aggressive mob
2 Switch to gamemode spectator or gamemode 4
3 Watch which mobs vanish.