"Hawkeye may have an unlimited number of specials placed on him until he is KO'd"
Is this legal to play from battlesite for the reserve char? I would assume no since it doesn't specifically state anything about the reserve.
Your assumption is correct, the special does not mention anything about the reserve so you cannot play the card on a reserve character (... in normal circumstances).
There is a related family of specials with code BR that allow you to gain one place slot from the reserve:
(http://overpower.ca/cards/specials/744.png)
Banshee and Forge also have this special.
Now the HH specials state no duplicates can be placed. The BRs only mention extra card. Couldn't find it in wiki or metas. Do BRs allow dupes?
If there is a legal way for the dupe to exist during the placing phase, yes, BR allows dupes.
When symbiotic samples taken event comes out, and starjammers has a BR played from a site, he can load up a 7 fighting and AP 7 too along with a third PC = sweet
(http://s.ecrater.com/stores/25172/4d04dde55d753_25172b.jpg)