Isn't Dead Sea dead boring? And Antony is the weirdo with the dog, right? Found both of them a little strange and boring, but I would've loved Vulpes Inculta as a companion.
I do love Dead Sea's reaction when I tell him to "carry on" though xD
Boone is boring yet people love him. :shrug:
And Anthony is just flat out weird... Which is why I want him.

But Vulpes?
He's like what? The fourth most powerful man in the Legion. (Caesar>Lanius>Lucius>Vulpes)
He can't be a companion, wouldn't make sense considering who he actually is.
I would love to have him as a companion as well but it's just not being very realistic.
Dead Sea on the other hand could always be told by Caesar to join up with The Courier and give a helping hand and let Severus take control over Nelson instead.
And Anthony... He's just weird... I'm sure that Caesar could allow him to join The Courier even if he is the hound master.
And hell, with the right back-story and personal quest those two could be incredible companions.
Sure Dead Sea is very very very militaristic and Anthony's voice is kinda like daggers to the ear drums but still, would be awesome companions IMO.