No way Fishman okays a Ghost collab.
I like Ghost, but I think the Ghost/Pippa interaction is at its best as it currently is: third party harassment of Ghost with vtuber stuff and mentions to Pippa about Ghost's current ongoings. It's the most humorous method of interaction between the two, and while an actual collab could be quite amusing, it's a long shot that they'd pull it off perfectly, and perfect would be needed for such a stream to not just be an unfunny awkward mess.