There really is no corralation between tail shape and aggressiveness. All the tail types are B. Splendens so the aggressiveness is all in relation to the specific betta's personality. I do not believe that they should be advertising that the VT can be housed with other fish just because that is not always true. I also think that CT may look more aggressive to some people because of the way their fins do compared to the VT whose fins mainly flow which makes them seem more calm.
If anything I'd think that a PK would be more aggressive as they are the closest relation to a wild Betta Splendens
In all actuality wild B. Splendens are not that aggressive. Most wild species of betta can easily live in a community setting both with other species of fish and others of their own species. Any of the domesticated B. Splendens or crossings with B. Splendens are the ones that have the aggressive nature. PK like the Superman and #5 PK are normally the ones that are reported to be the most aggressive but I personally have no idea if they are really anymore aggressive than a normal PK or even a VT.