I believe that might be needed, or you could get access violations (two instances accessing something at the same time).
But you could just update one, copy the entire thing in another directory at first, so you don't have to download the initial large update multiple times.
I did find some info that multiple servers can lead to not being able to VAC secure all servers.
Just google a bit if you get stuck.
__________________
Get a lid on that zombie,
he's never gonna be alri-i-ight.
Oooh get a lid on that zombie,
or he's gonna feed all night.