I had a playthrough where I was on the Alison path the entire time BUT chose to decline Alison for the trip.You don't have permission to view the spoiler content. Log in or register now.
She ends up going with Jeremy and Billy anyways. The phone call also happens and like the cuck path, there is also something going on the background: "Hey!" and Alison blushing etc.
So yea she kinda does the threesome anyways. The difference is that Jeremy does not send the video at all.
And yes it's weird that Alison sleeps with Jeremy in a playthrough where Ian has her all to himself. But at least the dialogue by Jeremy is interesting on this path. He basically warns Ian that he will regret not going on this trip with Alison. Nice touch by Eva for even considering this specific path.
edit: but what would have made it better would be to have Alison reject Jeremy and Billy on this path, and then have Jeremy calling Ian to tell him how he failed. That would make more sense because Ian has been showing affection to her the entire time.