The Chief? (I know that the era you're talking about is when John Byrne revived the original Doom Patrol, did they join the League during that story?)
no, and i'm not aware of the Doom Patrol joining the League. also not quite sure when the Doom Patrol were revived...
also no
Who does Kimiyo Hoshi bring with her to question the Shadow Thief? This happened after the League memberships of Blue Devil & Lightray, but before the membership of Cyborg. It happened after Nightwing's Obsidian Age membership, but before his later membership. John Stewart was also a member at that time.
It was a male Leaguer, and a legacy character.
The Shadow Thief had enhanced powers at the time; Kimiyo thought this Leaguer had the scientific expertise that could help her figure out those powers.
not:
Fire
Blue Beetle (Ted)
Hawkman
Green Lantern (Hal)
Batman
Atom
Captain Atom
Guy Gardner
Power Girl
Tasmanian Devil
Obsidian
Max Lord
Blue Devil
Cyborg
Nightwing
Lightray
John Stewart
any of the Flashes
Roy Harper
The Chief, or any of the Doom Patrol
any Steel