You should note that the source you linked above isn't a Wizards of the Coast site, but a fan maintained wiki. Dvati are a race that were last published in the Dragon Magazine compendium for 3rd edition D&D, but is not among the races that Wizards of the Coast have published for 4th edition. I've seen a few homemade adaptations for 4e when I did a search to recall it.
While its not precisely cheating to have one in a game (maybe you have a lot of homebrew stuff in the game already?) I'd be very wary of allowing one into one of my games.
From a balance standpoint, allowing a character to split their hit points and then get double the actions could break 4e's careful action economy. All the official character options that allow a single player to control more than one creature (summoning, animal companions, etc) limit them to sharing the number of actions that a regular PC gets. Normally a PC gets a move action, a minor action, and a standard action - and when they control a second creature, if they want the summoned creature or animal companion to attack the rules requires the player character to give up their attack.
I'd suggest you review what sources you're suggesting people use to make their characters, then take this up with your dvati player.