The /spreadplayers command does not work with entity UUIDs, it just prints the error message "Player '%s' cannot be found" (%s being replaced with the provided UUID).
- Summon an entity with a defined UUID
- Try to use the /spreadplayers command
→ It prints the error "Player '0-0-0-0-0' cannot be found"
Based on 1.11.2 decompiled using MCP 9.35 rc1
The method net.minecraft.command.CommandSpreadPlayers.execute(MinecraftServer, ICommandSender, String) does not use the method net.minecraft.command.CommandBase.getEntityList(MinecraftServer, ICommandSender, String) to parse the entity UUID / selector / player name. Instead it partwise implements the behavior itself.