Interesting story. Would love to see more photos. There was an experienced keeper who had a rescued male veiled that lived with her Melleri. He escaped and was found in their free range. When she tried to separate them he suffered. He wanted to be with them and they appeared to like his company. So I guess it can happen. Melleri are very social animals and don't seem to like to be singular. Panthers, on the other hand, are not.
Be watchful, as Melleri aggressive behavior can be very subtle. Even the head resting on the back of the Panther's neck can be a signal from a Meller's cham that they are in control. A sentiment that a male Panther may not appreciate. But they do appear to be resting comfortably in your photo.
It will be interesting to see how their relationship unfolds. But do watch as personalities can change as hormones cycle throughout the year.
Is this the Panther with the strange coloration that you cannot tell what locale it is?