Help..

If i use custom textures in a map and upload it to hell ZM will the textures be missing or will the map auto download the textures for the players when they join the server.

 

You need to attach them to the BSP. This can be done as the last step of the map as you have to do it after you've done the full compile.

You can use a software called VIDE to pack your custom textures.

Here's a detailed text tutorial:
http://www.tophattwaffle.com/packing-custom-content-using-vide-in-steampipe/

Once the files are packed to the bsp, anyone who downloads the bsp on the server will download the custom files with it.