Okay on scm draft and starforge there are units like "unused command center" and "cantina". Can you actually use these or do they just crash starcraft in game?
Most 'unused' units crash Starcraft when a player looks at them ingame (will only drop that one player). I can't seem to find it right now, but there used to be a list of which units crashed. Any of the non-crashing units will just be buildings that appear as Protoss Scouts.
You can use most of them for death counters though, if I'm not mistaken
You can use any unit for death counters, provided its unit ID is between 0 and 228 (inclusive). Otherwise the 1.13b patch on EUD actions prevents editing.