I don't know if it's ever been pointed out before, but in Masters of All Time it is actually confirmed that alternative! Vlad and Maddie knew all along about Jack's powers, as well as the fact that they were a result of the ghost portal accident.
Maddie: Oh, you're awake. Good, I have some questions for you. Let's start with 'who are you' and 'why are you snooping around my secret lab?'
Danny: Wait, what are you doing!? [The laser fires a fine green light of energized particles, the beam gets close to his arm pit.] Stop!
Maddie: Oh, scream all you want, ghost. This lab is totally sound proof; it has to be or my husband would find out about it. Now, I ask you again: 'Who are you?'
Danny: I'm- your son. [Maddie gasps.] Yours and Jack Fenton's.
Maddie: Liar! I haven't seen Jack Fenton in years. He blamed me for the accident that gave him his powers, Vlad told me so; we ran away here to escape his ghostly wrath.
Danny: What? That's insane! He's still totally in love with you.
Jack: [Phasing in from the ceiling.] It's true, Maddie. It's always been true.
According to Maddie, she believed Jack resented her all along and would not be above using his ghost powers to get revenge on her because Vlad told her so.
But the very important thing to keep in mind is the fact that Vlad knew about his ghost half at all, in the first place. Because, yes, after Danny altered the timeline, the two of them saw Jack's face being covered in ecto-acne, but that alone doesn't prove anything because so did the original Jack and Maddie when Vlad suffered his own accident, and yet, they never knew about his ghost powers.
This in turn would suggest that, unlike our Vlad, who spent a long time in the hospital and then cut all contact from them for years, zealously keeping his ghost half a secret; Jack actually told him and Maddie (or, at the very least, Vlad) about his ghost powers upon gaining them, probably hoping they could help him or that the three of them together would be able to find a cure. With Vlad then twisting that knowledge into a sick lie to keep Maddie close and away from Jack.
Where am I trying to get at with this?
Simple. If Vlad had been a better person and helped Jack with his powers, chances are phanon's ghost-hunting College Trio would have come to be, further reflecting Danny, Sam, and Tucker in the main timeline.
