It is unlikely that the light would generate a TCAS contact as Mr Nasty would no doubt have turned off his transponder thereby making TCAS useless. They did it on 911 and ATC lost primary radar contact or just couldn't monitor the exact contacts they had.
All ATC would do is call an unknown primary conact and issue any avoiding action they felt necessary if it was felt that the contact was actually an aircraft (depending on the type opf airspace)