As Marion is back, plus it seems the Ark is back in some capacity, plus Abner's story is pretty unknown to say the least, plus Hurts age, then it seems more than likely that Hurt will indeed be Abner.
His obsession was the Ark: if the Ark is back and linked to the crystal skulls in the movie, then its reasonable that Abner will be at the forefront of this research.
Something tumultuous must happen for Marion to be returning: if the rumour that she's used by the Russians to blackmail Indy into action is true then it would be "more" believable that they'd traced her and Indy's past through having Abner already rather than for some godforsaken reason know about her past flings.
Abner's history and fate have in no way been spelled out to us in the previous movies: we know he was long gone in Nepal in Raiders in '36 which doesn't mean he died as enough ambiguity exists in the dialogue of this original scene to leave things open-ended.
Hurt is currently a very weathered 67 (facially): if he plays a character even his own age (and obviously he could easily play older) then that would be 9 years older than Indy in 1957, the assumed setting period. As Indy is known to be much older than Marion (from the dialogue in Raiders),then this puts Hurt;s character at least 20 years older than Marion, so its possible he's a realistic choice to play her dad.
All things considered I think there's little chance he's not Abner, and I think its a great plot idea to have him back.
'Course, this could be totally wrong as recently Darabont claimed he persuaded the Beards to bring Marion back. I can't see this ALSO resulting in bringing Abner back, which suggests he was in the story already. And I can't imagine a storyline for Indy 4 that included Abner but not Marion. Then again, thats supposing the key elements of the Darabont storyline remained through the Nathanson and Koepp re-writes, which for the record I'm inclined to believe (I think it was the tone and characterization aspects of a Darabont script that would peeve Lucas - a bad thing for the movie IMHO).
Which brings my tortuous logic back to its conclusion that Hurt is almost certainly Abner!