Is Desktop Manager compiled with kernel in iso distribution files

I'm trying to see the process of redistributing a linux distribution. I was wondering if all the components are compiled with the kernel or kernel is seperated from components like is Desktop Manager compiled with kernel or i should place the DM packages in the iso file and the installer has to install it after the kernel or maybe other ways! Sorry im new in this but i have experience in compiling, developing and mid level programming and im willing to do it at least in the minimal way. I appreciate any explanation, suggestions, guidance any thing that can help to get started