Yes its a package in the software and you cannot separate it.
If you install Tableau server 2018.1 below will be tabadmin, and 2018.2 above is TSM.
i have bought Tableau creator licence .tabcmd will come with licence itself
For versions 2018.1 and older (e.g. 10.5) tabcmd can be used on other machines: tabcmd
For version 2018.2 and newer tabcmd can be used on other machines: 2018.2 tabcmd
It is not mandatory to install it on the same machine as the Tableau Server, however, it won't hurt anything to do so. You can have it installed in multiple locations as there is no licensing limitation.