also Greedo's line about the bounty hunters looking for him is no indication of if he's a Bounty Hunter or not. He said every bounty hunter is gonna be looking for Han (if greedo's a bounty hunter this would include him) and the he is lucky he (as a bounty hunter wanting the bounty on Han like all the rest of the bounty hunters) is lucky he was the first bounty hunter to find him (though ends up being not so lucky for him)
of course that take assumes he's a bounty hunter and im not discounting your idea, more trying to show how that part of the conversation doesnt support it either way. but after reading the above mentioned story in Tales, I would say he's a bounty hunter.
the part that always intrigued me is Greedo telling han if he gives him the money he would forget he found Han. Thats a pretty ballsy move no matter who you are (bounty hunter and/or lowly employee of Jabba) if Jabba were to find out you took his money and ran off (which is whats implied by that statement, because if his plan was to give the money to Jabba he wouldnt be forgetting that he found Han) you would be more hunted than Han was. So i always found it interesting that Greedo made this comment.
also, just though of this now, but just because Han calls Jabba Greedo's boss doesnt mean Greedo is in direct employ of Jabba. Technically when Fett (or any bounty hunter) takes a job from someone (anyone) for a bounty he is working for the person that put out the bounty.
-Darth Simon