What on earth is Mainstream talkin' about?
2 Green Goblins a once? Lets not forget that the whole time Harry Osborn was the Green Goblin is the classic comics, Norman Osborn was actually alive and well, hiding in Europe.
Therefore, in the original, Noman went into hinding and was presumed dead by the general public; then his son Harry took his place as Golbin II.
In Ultimate Spiderman, Norman has been placed under arrest by S.H.I.E.L.D and could well be presumed dead by the general public. As far as the characters in USM know, Norman Osborn isn''t coming back (although we all susspect he'll be back sooner than later) Therefore, it makes perfect sense of Harry to replecace him a Green Goblin II.
If U. Hobgoblin's skin was green instead of yellow, my view would be easier to see.
... And who actually refered to Ultimate Hobgoblin as "Hobgoblin", was it Harry, Peter, or was it simply presumed that was his name?
Where do they come out and say he's the Hobgoblin. It's just in the title. He never comes out and says "Rrrargh! I am the Hobgoblin." He just becomes a Goblin like his dad, but it looks kinda orange. It's like Ultimate Carnage, no name listing they just expect people to know what they're doing despite having completely changed the origen.