Don't forget they would of also been running and hiding from the Empire staying one step ahead.
Hoth was probably one of many places they'd been. Wasn't Ord Mantell given as the place Solo ran into one of jabba's bounty hunters.
Also isn't there a line from early on when Vader is seeing the footage from the probe droid and says that it's the Rebels and "Skywalker is with them" or am I confusing the with the radio dramas?
No, you're right. He either says 'That is the one and Skywalker is there' or 'That is the one and Skywalker is with them.' I've never heard the radio drama but remember that from the movie.
As for the main topic (joining it very late), there's a comic called Vader's Quest, in which he gets the name Skywalker after torturing it out of a rebel source. While I'm no EU fan, that works for me. I've always assumed that he wasn't so stupid as not to make the connection. Especially given his own comment that the force was strong in that pilot, during the Battle of Yavin.
As for the amended dialogue in ESB Spec Ed, it only makes sense if you accept that Vader was playing innocent to the Emperor and pretending that he was unaware of who the young pilot really was. Given that Vader's obsession with finding Skywalker is mentioned in the opening scroll, he must have known that this was his son. Even if you accept that Vader is a complete idiot (perhaps not that hard to assume, having seen the PT!) and hadn't actually realised that the force strong pilot bearing his name was his son, it's hard to see any other reason for his obsession for finding the young rebel. Revenge for the Death Star? Not really, that was Tarkin's pet project. Vader warned that it was no match for The Force.
But for all that the new dialogue ties in with the scheming nature of the Sith and their constant plotting against each other, I still prefer the dialogue in the original ESB. I've no problem with Lucas inserting Ian McDiarmuid into the movie for the sake of continuity, but I don't know why he didn't leave the original dialogue intact.