Does zombie mod work, and If so how to get it working? I don't know how to use the mods on the bot_mods.ini file, and I can't find tutorials about it.
zombie mode is only for mods that are not fully supported by the bot. It will only work if the mod allows players to join without any complicated team joining system, such as selecting team/class etc. The zombie bot simply runs towards every other player and hits the attack button. To be honest, never had to try it or test it...!!!
to use bot_mods.ini simply choose bot type as ZOMBiE for the mod you want, for example HL2DM zombie will be
Is this for Windows servers?
Did you try going to Launch Options and adding "-insecure" for that game? Also you may need to check if you need to use "sv_cheats 1" to see if those bots appear properly.