Other Speedrunners used some mods like a timer in the past. Is that allowed? If so, could we use a Zombie count mod for our speedrun?

The timer is just an external program called LiveSplit. The rules state specifically not to use any plugins, so I think it's probably not allowed.

Edit: After looking a bit of runs, it does look like some use an in-game timer plugin. But, I'm still not really sure about zombie counts.

zombie counter is NOT allowed