As far as I know, the answer is yes. Visitors in other experiments (control group or not) will be excluded.
John - This is also my understanding. Løjmann is correct: it doesn't matter if it's the control or one of the test variants -- they would still be considered entrants from another test.
Thanks guys, this is what I assumed but I was hoping there would be some documentation to confirm that.
I've search high and low, as I'm sure you have too, and cannot find any documentation related to visitor: not in other tests. Perhaps your Target consultant can provide a definition.