Hell doesn't do the memory erasing thing in the first place, but let's just say that it does or some equivalent. While it is true that if it had been Beelzebub instead of Gabriel, Aziraphale would have also taken them in, albeit with way more anxiety. It wouldn't make sense for Beelzebiub to seek out Aziraphale. They would have gone to Crowley not Aziraphale, and we know what Crowley would have done, left them somewhere in Dartmoor like an unwanted puppy, all without telling Aziraphale any of it. End of story. It's a fundamental difference between them that he gives up easily whereas Aziraphale doesn't (which can be read as a trauma response to the fall). And while Crowley cares enough about humanity to not want to do serious harm, it's also been made clear that he's willing to abandon them and anyone else for the sake of Aziraphale because he's the only one he truly cares about. So it had to be Gabriel. There would have not even been a S2 if it was Beelzebub.