I think what would happen is that Rogue would gain Spider-Man's powers that the alien still had: Super strength, agility, spider sence, organic webshooters. She would also gain the emmediate knowledge, and all the knowledge that the alien kept when it was seperated from Peter, all the knowledge from Eddie Brock, all the knowledge of Scorpion, and all the knowledge that the alien gain its whole existance (all the knowledge of the universe it had), and all at once too.
It would be too much for her and it would be too much for the alien. I mean she would essentially receiving three or four, or more, personalities all at once. Rogue is thrown back from the alien and in great pain.
The alien on the other hand, would be mildly hurt. Sort of stunned and agitated now. While Scorpion, inside the alien, would be perfectly fine and unharmed.
She probably only gained small parts of the knowlege like Peter's and Eddie's and Scorpions, and maybe a little from the alien,
she would also gain spider-strength, agility, and web shooters. (and still look human)
But it would probably only be for a short time.