No.
See here: http://www.teeworlds.com/forum/viewtopic.php?id=4852
It is a little different, because you're talking about open slots and not players, okay. Well you have to make sure if a slot is offered that it is available to everyone, except if you put a password. Some servers don't respect that but most reserved slots don't advertise bad slots (hence servers with 15/14 players sometimes).
Some old implementations of reserved slots don't take this into account, but as long as there is no fake players and it's a modded gametype (and malicious) we don't really care. The best way is still to make sure your slots are available (like in zombie mod or others).