Hey René,
If you haven't read this it's worth a couple of minutes of your time.
Tip: How Do I Get The Best Answer in the Shortest Time?
And don't forget to search the forum – there are several threads on iTerm.
All you can do with Keyboard Maestro in this context is insert text (either by typing or by pasting) and mimic the Return key.
This will usually work just fine if you've set things up properly, but since you're driving the UI an unexpected chuckhole might cause an accident.
Therefore a scripted solution is usually better and more foolproof (when available), because it acts with the application in question rather than on it.
AppleScript terminology is generally different for different applications, so you usually can't mix and match app-specific code – and that's why you couldn't simply trade “iTerm” for “Terminal”.
Here's an AppleScript that works with iTerm 3.2.7 on macOS Sierra 10.12.6.
Run from an Execute an AppleScript Action.
----------------------------------------------------------------
set cmdStr to "vifm"
tell application "iTerm"
tell front window
tell current session
# Attempt to discover if current session is busy.
if name = "bash" then
write text cmdStr
else
false
end if
end tell
end tell
end tell
----------------------------------------------------------------
-Chris