First and important note, hector_slam is a metapackage. It includes hector_mapping and related packages.
If you want to install a package or a metapackage you can use install from the source option. As you mentioned, you need to use your distro when you want to install a package
sudo apt-get install ros-kinetic-hector-slam
Method 1:
You can be sure about that you've installed the specific package when you use the 'from the source' installation method by simply cheking the installation folder of the packages.
So simply go to "/opt/ros/kinetic/share" folder by typing this:
cd /opt/ros/kinetic/share
if you want to list all of the hector_slam metapackage packages, you can list them with grep:
cd /opt/ros/indigo/share && ls | grep hector
Method 2:
if you want see the packages are installed or not, you can use rospack find command. It will give you the location of the package. For example type this to the command line,
rospack find hector_mapping
But if you try to search directly hector_slam, it will say it's not installed. Because this command doesn't work with the metapackages. You can use this command to find your manually installed or created packges.
Method 3:
You can use the roscd command to go directly to the installation directory if the package is installed. For example:
roscd hector_mapping
then type pwd to see which directory that you're in.
I hope this answer is satisfying for you. If you have any question about hector, you can ask as well.
Note: You can find other packages with typing it's name instead of typing 'hector_mapping'.
